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Full text of "A montane rain-forest; a contribution to the physiological plant geography of Jamaica"

A MONTANE RAIN-FOREST 



A CONTRIBUTION TO THE PHYSIOLOGICAL 
PLANT GEOGRAPHY OF JAMAICA 

By FORREST SHRE\ 





-ryr 



HREVE 



PUt. 




p 

E 

u 



A MONTANE RAIN-FOREST 



A CONTRIBUTION TO THE PHYSIOLOGICAL 
PLANT GEOGRAPHY OF JAMAICA 



BY 



FORREST SHREVE 




WASHINGTON, D. C. 
Published by the Carnegie Institution of Washington 

1914 



\J 



5. 



CARNEGIE INSTITUTION OF WASHINGTON 
Publication No. 199 



Copies of this 8ook 
were first iMUed 

SEP12 19U 



PRESS OF GIBSON BROTHERS, INC. 
WASHINGTON", D. C. 



CONTENTS. 



pac::. 

Introduction 5 

The Physical Features of the Rain-forest Region 7 

General Climatology of the Rain-forest Region 10 

Air Temperature 10 

Nocturnal Terrestrial Radiation 11 

Soil Temperature 12 

Humidity and Fog 13 

Rainfall 13 

Sunshine and Cloudiness 16 

"Wind 17 

The Flora of the Rain-forest 18 

The Vegetation of the Rain-forest 22 

Ecological Characteristics of the Rain-forest 22 

Habitat Distinctions in the Rain-forest l2 > 

Windward Ravines 28 

Windward Slopes 31 

Leeward Ravines 32 

Leeward Slopes 33 

The Ridges 35 

The Peaks 37 

Epiphytes 38 

The Relation of Physical Conditions to Habitat Distinctions in the Rain-forest. ... 41 

Humidity 44 

Evaporation 46 

Air Temperature 18 

Soil Temperature 

Seasonal Behavior of the Rain-forest Vegetation 51 

Rate of Growth in Rain-forest Plants 55 

Transpiration Behavior of Rain-forest Plants 59 

Methods and Material 59 

Daily March of Transpiration 62 

Individual Variability of Transpiration Rate 72 

Concurrent Rates of Transpiration in Different Species 73 

Relative Transpiration 76 

Comparison of Relative Transpiration Rates in Rain-forest and Desert Plants. . . 82 

Relative Amounts of Stomatal and Cuticular Transpiration v ~ 

Stomatal Behavior 

Influence of Darkness on Transpiration 

Influence of High Humidity on Transpiration 102 

General Conclusions 106 

3 



INTRODUCTION. 

The vegetation of Jamaica is of particular interest, both by reason 
of the wealth of the flora of which it is made up and because of the 
diversity which is given it by the varied geological, topographic, and 
climatic conditions which exist within the limits of so small an island. 
Jamaica lies in the center of the Caribbean Sea in 18 N. latitude, is 
about 150 miles long, and from 25 to 50 miles wide. Its most salient 
physical feature is the central mountainous axis, the eastern end of 
which is lofty and of relatively recent geologic age, while the western 
two-thirds are lower and older; the recent formations being mostly 
shales, conglomerates, and tuffs, the older limestone. The mountain- 
ous interior is bordered on the north by a very narrow coastal plain, 
on the south by a plain which is narrow opposite the loftier mountain 
mass, but wide in the southwestern parishes of the island. The higher 
elevations of the eastern end constitute the Blue Mountain Range, 
which attains to an altitude of 7,428 feet (2,264 meters). Not only 
do the Blue Mountains present conditions of temperature that result 
in their own vegetation being distinct from that of the lowlands, but 
they moreover serve as a barrier to the trade winds, and thereby give 
differences of rainfall and humidity on their north and south sides which 
are of importance in determining the character of the lowland vegeta- 
tion. The greatest rainfall in the island is registered at high elevations 
on the northern slopes of the Blue Mountains, while the least occurs at 
the coast to the south of them. The lower and older portion of the 
mountainous axis, which reaches its highest points in Mount Diablo, 
Bull Head, Dolphin Head, and the Santa Cruz Mountains, is much less 
diversified than the Blue Mountains in both temperature and rainfall 
conditions, and strikingly dissimilar to any part of them in its vegetation. 
South of the older mountainous region are broad savannas, with morasses 
along the larger streams and deserts on certain parts of the coast. 

There is perhaps no tropical area of its size in the world that has 
received more painstaking and prolonged attention at the hands of 
collectors and taxonomists than has Jamaica. From the reconnais- 
sances of Sir Hans Sloane, the first botanical visitor to the island, in 
1687, down to the methodical campaign which has been made during 
the last twenty years against all the less-known parts of the island, 
there has been a steady stream of additions to the flora, in which over 
forty botanists have taken a hand. During these two centuries of 
floristic activity there has been, however, but a single visitor interested 
in the vegetation of the island in its physiognomic and physiological 
aspects, the Danish botanist Orsted. He visited the island in 1846 
and published a paper entitled "Skildring af Naturen paa Jamaica."' 
which is a brief description of the vegetation, strikingly modern in its 
manner and as accurate as his brief visit of six weeks would permit. 



6 A MONTANE RAIN-FOREST. 

In spite of the facl thai Jamaica was the first portion of the Western 
Hemisphere to reach a high and valuable agricultural productivity, 

there is still much of it that lias been left untouched by the Spanish 
and English occupants of the island, either because of its inaccessibility 
or of the worthlessness of both the land and its natural covering. These 

are the very localities which are most interesting to the botanist, 
because of their being the places where the factors controlling plant 
occurrence are operating in the most extreme degree. The higher 
Blue Mountains, the limestone mountains of the central region, the 
exsected limestone region known as the "Cockpit Country,'' the coastal 
deserts, the morasses and the mangrove swamps, as well as the algal 
formations, are all calculated to interest the student of vegetation in 
the highest degree. 

During three visits to Jamaica I have had opportunities to see some- 
thing of all the above-mentioned formations, excepting the larger 
morasses and the heart of the Cockpit Country, and have been able 
to spend a total of eleven months in the Blue Mountain Region at 
Cinchona, the Tropical Station of the New York Botanical Garden. 
Cinchona is situated on a spur projecting south from the Main Ridge 
of the Blue Mountains, at an elevation of 5,000 feet (1,525 meters). 
I first visited it in April 1903, in company with Dr. D. S. Johnson; 
for the second time from October 1905 to May 1906, while holding the 
Adam T. Bruce Fellowship in the Johns Hopkins University; and for 
the third time from July to November 1909, while absent from the 
Desert Laboratory. 

My last tw r o visits to the Blue Mountains have been given to gaining 
an acquaintance w r ith the common and characteristic components of 
its flora, to a study of the distribution of the vegetation within the 
mountain region, and a study of the differences in physical conditions 
which underlie the distinctness of the several habitats, as well as to 
an investigation of some of the physiological activities of plants con- 
fined to the rain-forest region. In the following pages I am presenting 
my results on the general physiological plant geography of the Rain- 
Forest Region, as well as my investigations on transpiration and growth 
in typical rain-forest forms. 

I wish here to thank Dr. N. L. Britton, Director of the New York 
Botanical Garden, for the facilities and equipment which were put at 
my disposal in Jamaica by the Garden. To Dr. D. T. MacDougal 
and Dr. D. S. Johnson I wish to express my thanks for their personal 
interest in my work during both visits. I wish also to thank the Hon. 
William Fawcett, former Director of Public Gardens and Plantations 
of Jamaica, for many substantial kindnesses show r n me during my 
second visit in the island; and to William Harris, esq., Superintendent 
of Public Gardens and Plantations, my thanks are due for assistance 
in taxonomic matters as w r ell as for many services essential to the 
prosecution of my work. 



THE PHYSICAL FEATURES OF THE RAIN-FOREST REGION. 

The Blue Mountains lie in a WNW.-ESE. position, being midway 
between the north and south coasts and parallel with them. The range 
extends from Silver Hill in the west to Cunhacunha Pass in the east, 
a distance of 22 miles. The first considerable elevation in the western 
end is John Crow Peak (6,000 feet, 1,830 meters), which is separated 
by Morce's Gap (4,934 feet, 1,505 meters) from a comparatively level 
ridge which runs from an unnamed elevation (about 5,800 feet, 1,770 
meters), through New Haven Gap (5,600 feet, 1,705 meters), Sir John 
Peter Grant Peak (about 6,200 feet, 1,890 meters), and Mossman's 
Peak (about 6,900 feet, 2,105 meters) to Portland Gap (5,550 feet, 
1,695 meters). To the east of Portland Gap the ridge rises abruptly 
to its summit in Blue Mountain Peak (7,428 feet, 2,265 meters). From 
its sister peak, the Sugar Loaf, the range descends gradually eastward 
to Cunhacunha Pass. To the north and south of the Main Ridge, 
lesser ridges diverge toward the sea, dropping in altitude with a rapidity 
which may be judged from the fact that the coast is in no place more 
than 13 miles from the Main Ridge. To the east of Cunhacunha Pass 
lies the Blake, or John Crow, range, running parallel to the eastern 
coast and having an average elevation of about 2,100 feet (640 meters). 
Again, to the south of the Blue Mountains lies a range known in part 
as the Port Royal Mountains, which have their greatest elevation in 
Catherine's Peak (5,036 feet, 1,535 meters) and rise to nearly that 
height at other places. 

In the following pages I have confined my treatment to the Blue 
Mountains proper above an elevation of 4,500 feet (1,372 meters). On 
descending below this altitude the flora of the mountains is rapidly 
left behind and the climate is found to be not only warmer but drier 
and less foggy, at the same time that the virgin forest begins to give 
place to vegetable and coffee fields. The accompanying map (plate 1) 
has been drawn from Liddell's survey (published by Stanford) and the 
contours have been sketched in from eight known elevations. The 
contours have been used only for the sake of giving a graphic approxi- 
mation of the extent and configuration of the area under consideration. 
The roads and trails indicated are the only ones in the area, and the 
character of the topography and vegetation makes it laborious to pene- 
trate very far beyond them. Although I have made visits to Portland 
Gap and Blue Mountain Peak, the region is best known to me in its 
western part between John Crow and Sir John Peaks and between 
Cinchona and Vinegar Hill, and it is within this part that all of my 
instrumentation has been carried on. 

7 



8 A MONTANE RAIN-FOREST. 

There are no traces of recent volcanic activity in the Jamaican moun- 
tains and they present to-day the rounded summits and closely set 
valleys of B typical erosion topography. The underlying rock is 
mainly readily weathered shale. At the summit of John Crow Peak 
and at a few localities in the Clyde and Green River valleys there are 
outcropping* of limestone. In spite of the copious rainfall there are 
no constant streams above 4,500 feet, but at a very few hundred feet 
below that elevation the water table emerges to feed numerous swift 
streams. Owing to the nature of the topography, there are no lakes 
or ponds, although there are a few depressions on the summit of the 
Main Ridge itself, which are developed as sphagnum bogs. 

The longer lateral ridges which form the divides between large 
drainage areas are comparatively gentle in slope (14 to 25). Those 
ridges which separate smaller drainage areas are steeper (25 to 35). 
The flanks of these ridges are, of course, steeper still (35 to 45) and 
in narrow ravines the sides are frequently as steep as 65. Such 
precipitous slopes, in the absence of resistant rock, are a resultant 
between the erosive action of the abundant rainfall and run-off and 
the retaining action of the vegetation. The former of these forces fre- 
quently overcomes the latter and landslips take place which devastate 
the vegetation and leave paths which remain unstable and bare for a 
long time. 

The deepest of the soils is a yellow clay w r hich occurs on ridges and 
gentle slopes in a few localities in the vicinity of the limestone outcrops, 
and sometimes attains to a depth of 8 feet. With this exception the 
soils are shallow and filled w r ith coarse rock fragments. Their humus 
content is high, but the rapidity of erosion prevents its accumulation. 

The climate of the Blue Mountains is that of all mountainous regions 
in tropical islands. The temperatures are extremely constant and low 
as compared with those in the lowlands, although very rarely so low 
as to make frost possible, and the rainfall is abundant at all seasons. 
The Blue Mountain Region is, therefore, a tropical montane region, 
in the terms of Schimper, lying above the hot lowlands and not attain- 
ing to a sufficient altitude for alpine influences to come into full play. 
The dominant vegetation is, in accordance with the climate, the ever- 
green broad-leaved forest, w r hich is here of a type strongly temperate 
in its floristic make-up and in its vegetative characteristics. 

The economic value of the forests and lands of the Blue Mountain 
Region is low, as has been hinted in the Introduction. A very small 
amount of timber is taken out of the forests from time to time to supply 
the framew r ork for bamboo houses in the neighboring settlements, but 
the bulk of it stands to-day untouched. Although there are several 
valuable woods among the mountain trees, notably that of the Podo- 
carpus, natural obstacles make the forests commercially worthless and 
they are held as Crown Land for the sake of their value as a cover and 



SHREVE 



Pht? 2 




PHYSICAL FEATURES OF RAIN-FOREST REGION. 9 

a source of water supply. At present the only extensive agricultural 
operations in the Blue Mountains are the planting of Arabian coffee, 
which grows successfully on the southern slopes up to 4,500 and 5,000 
feet. Above this altitude, and on the northern slopes, it grows well 
but does not bloom and produce berries abundantly enough to be 
profitable. Assam tea grows well at from 4,800 to 5,500 feet, but has 
never been planted extensively. For a number of years the cultivation 
of Cinchona, or Peruvian bark, was carried on very successfully at 
from 4,500 to 5,900 feet, and there are now no natural obstacles to its 
production, indeed Cinchona officinalis has become naturalized in the 
vicinity of some of the old fields. On the southern slopes, from 5,000 
feet downward, at least one-third of the land is out of cultivation and 
covered with a scrub of xerophilous bushes, known locally as " ruinate." 
Indications point to the reforestation of the ruinate as being a very 
slow process, as some of it which has not been touched for twenty-four 
years is far from having the beginnings of a stand of forest trees. 

The precipitate slopes on which coffee is grown are very liable to 
landslips. During the heavy rains of November 1909, hundreds of 
acres of coffee were destroyed in this way, and the areas they occupied 
must remain unstable and bare for many years. The landslips that 
were conspicuous in April 1903, when I first visited the Blue Mountains, 
were still bare of vegetation when I last saw them in November 1909. 
The heavy rains of that month did not cause an enlargement of the 
old landslips, but created new ones, some of which reached up into 
the virgin forest, where as a rule only small landslips occur. In the 
vicinity of Cinchona I have seen areas of ruinate, in which there were 
numerous landslips, that I was told, on creditable authority, were 
abandoned as coffee fields over fifty years ago on account of the exces- 
sive erosion. The indications are that the precipitate topography of 
the coffee-growing region will ultimately lead to its abandonment for 
all uses except the growing of vegetables, which is now carried on 
extensively by the negro peasants. The yam, the coca (Colocasia 
antiquorum) , the sweet potato, the turnip, the parsnip, and a small 
onion {Allium fistulosum) are all successfully grown in small patches 
protected from erosion by abatis of twigs and sticks. 



GENERAL CLIMATOLOGY OF THE RAIN-FOREST REGION. 

The following data on the climatology of the Montane Rain-Forest 

region are based on the record- kept at ( linchona, at New Haven ( lap. 
and at Blue Mountain Peak by the Jamaican Department of Public 
( rardens and Plantations, which are the only records ever kept in the 
higher Blue Mountains. The observations made at these localities 
were published currently in the Bulletin of the Botanical Department 
of Jamaica and in the Jamaica Gazette, but have never been subjected 
to a systematic analysis. I have secured data for several features 
(such as the number of rainy days) by an inspection of the manuscript 
records of the Department. 

Using these data as a basis I have endeavored to determine to what 
extent the physical conditions in certain typical plant habitats depart 
from the climatic conditions of the region as a whole, and in just what 
respects the several habitats differ from each other. I obtained records 
with an air thermograph, a hygrograph, a soil thermograph of the 
Hallock type, and at mo meters of the type devised by Livingston. 
These results will be presented in the chapter on the relation of physical 
conditions to habitat distinctions (see p. 41). 

AIR TEMPERATURE 

The record of air temperatures for Cinchona consists of daily readings 
of the maximum and minimum and of the current temperatures at 
7 a. m. and 3 p. m. In view of the constancy of temperature conditions 
a digest of these records for fifteen years (1891-1905 inclusive) has 
seemed sufficient to give an accurate set of means and ranges. Owing 
to the unfortunate custom of making a reading at 3 p. m., it has been 
necessary to determine the daily mean by taking half the sum of the 
minimum and the 3 p. m. temperatures. 1 In table 1 are exhibited the 
principal elements of the climate as respects temperature. 

At New Haven Gap a set of observations of the monthly absolute 
maximum and minimum was taken during the years 1882 to 1893 at a 
cleared spot in the summit of the Gap at 5,600 feet (1,705 meters) 
elevation. During the twelve years of these observations there are 26 
monthly readings missing. A set of observations of absolute monthly 
maximum and minimum was also taken at Blue Mountain Peak during 
the years 1890 to 1900, the instruments being exposed upon the cleared 
summit of the peak at an elevation of 7,428 feet (2,264 meters). From 
this record two months are missing. For the sake of comparison I 
have found by inspection the absolute monthly maximum and mini- 
mum for Cinchona for the years 1891 to 1900, and table 2 exhibits the 
means of these data for the three localities for the years mentioned : 

The absolute maximum for Blue Mountain Peak is 76 in September 
1891, the absolute minimum 33.3 in February 1893 ; the absolute maxi- 

iHann. Handbook of Climatology, Transl. by War*, p. 8. New York, 1903. 
10 



SHREVE 



Plate 3 




A. Looking east along the leeward slopes of Mossman's Peak and Blue Mountain 
altit uilr of 5,500 feet. The white areas are coffee fields. 



Peak from 




H. Looking southwest from tin 



vicinity of Cinchona into the valley "I Clyde River. 
< 'tom Peak are on i he li^lit . 



Sit 'i ies i 't .lolin 



CLIMATOLOGY OF RAIN-FOREST REGION. 



11 



mum for New Haven Gap is 83 in July 1889, and the absolute mini- 
mum 40.5 in January, February, and April 1888. Not only are the 
averages of the monthly absolute maxima and minima unsatisfactory 
data from which to determine the temperature conditions for a locality, 
but the fact that these figures do not cover the same years in the case 
of New Haven Gap as for the other localities invalidates too close com- 
parison of them. The more exposed position of New Haven Gap on 
the Main Ridge, as compared with Cinchona, will account for its 
greater range of temperature, the difference in altitude being but 600 
feet. Between New Haven Gap and Blue Mountain Peak there is a 
greater difference in altitude (1,828 feet, 555 meters); while the tem- 
peratures range lower at the latter place the annual and daily ranges 
are probably nearly the same. 

Table 1. Monthly mean temperature data for Cinchona, 1S91 to 1905. 



Monthly absolute maximum . 
Monthly mean maximum . . . 

Monthly mean 

Monthly mean minimum . . . 
Monthly absolute minimum . 
Daily range 



Jan. 



73 

66. G 

58.8 

53.4 

46 

13.o 



Feb. 



75 

67.0 

58.3 

53.7 

46 

13.3 



Mar. 



Apr. May, 



ta 77 
67.0 67.51 
58.6 59.3 



53.9 

47 

13.1 



55.3 

47 

12.2 



74 

68.3 

61.0 

57.3 

50 

11.0 



June. 



76 

69.9 

62.3 

58.3 

50 

11. e 



July. 



79 

71.9 

63.1 

58.8 

52 

13.1 



Aug. 



80 

71.8 

63.6 

58 8 

54 

13.0 



Sept. Oct 



75 

70.6 

62.9 

59.3 

51 

11.3 



74 

68.7 

61.8 



Nov. 



75 

68.3 
61.0 



58 7 57.3 



54 
10.0 



51 
11.0 



Dec. 



72 

66 
59 
55 

47 
11 



Annual mean temperature 60.8 (16.0 C). 

Annual mean range 5.3 (2.9 C). 

Average daily range 12.0 (6.6 C). 



Table 2. Monthly absolute maximum and minimum temperatures 

Haven Gap, and Blue Mountain Peak. 


at Cinchona, New 




Jan. 


Feb. 

71.4 
65.7 
67.0 

49.6 
46.0 
40.9 


Mar. 


Apr. 


May. 


June. 


July. 


Aug. 


Sept. 


Oct. Nov. 


Dec. 


Maxima: 


70.3 
69.1 
69.0 

49.5 
47.4 
38.3 


70.9 
72.2 
69.1 

49.3 
46.8 
42.7 


72.3 
73.7 
70.0 

50.9 
48 2 

40.8 


72.5 
75.2 
68.5 

53.3 
50.3 
44.6 


74.0 

76.3 
70.0 

54.9 
52.9 
45.6 


75 . ! 
76.0 
68.5 

55.4 
54.3 
46.1 


76.(1 
74.6 
70.4 

55.8 
55.3 
45.5 


74.2 
77.5 

71.3 

56.3 
55.0 
45.7 


72.8 72.2 
71.7 72.7 
70.2 

55.2 53.3 
54.6 51.1 

45.9 42.2 


70.5 
70.6 
68.8 

50.3 
47.4 
39.3 


Blue Mountain Peak .... 
Minima: 

New Haven Gap 

Blue Mountain Peak. . . 



NOCTURNAL TERRESTRIAL RADIATION. 

Several observations were made on nocturnal terrestrial radiation, 
with a view to determining what are the probable temperatures at the 
surface of the ground at the time of some of the low minimum winter 
temperatures. Ordinary thermometers were laid on a grass sod or 
lightly covered with earth on a flower bed; another thermometer was 
placed 3 feet from the ground and compared with a standard ther- 
mometer in a Stevenson screen. 



12 



A MONTANE RAIN-FORES 



In L906 the night of January 12 was clear and -till ; thai of February 
28 was dear with a high wind; that of January 13 was clouded and still. 

The readings were a- follow-: 

Table :>. 







Air 


On 

(.'Hi . 


'' lltll. 


1 nfference 


I difference 


Date. 


Time. 


temper- 
ature. 


between ;iir 
and earth. 


between air 
and Era 


January 1-' . . 


'.>' 00"' p.m. 


:.t 


60 :i 


49.6 


4.4 






ID 1 ' 00" p. in. 


55 


50 :; 


i> .; 


; 7 






ll h <)'>" p.m. 


54 


47.6 


46.7 


7 :; 




January 13. , 


9 !l 4.7" pin. 


59 


:.:, i 










in' nil'" p.m. 


50 


55 l 






6 


February _'v 


& :>()"' p in. 


59 




In :, 


10 :, 






10 h 30' p.m. 


55 




lit r, 


5 l 





These observations, taken on the open lawn at Cinchona, show that 
the temperatures to which herbaceous vegetation in open situation- 
may be subjected are as much as 10.5 lower than the recorded air 
temperatures on clear nights when active radiation is possible. The 
fact that radiation takes place most actively during the early hours of 
the night, while the minimum temperature is always reached just before 
daybreak, makes it necessary to derive the lowest temperatures due to 
radiation by subtracting 10 or thereabouts from a temperature higher 
than the lowest minimum as shown by the records of monthly extremes. 
This would still indicate the possibility of occasional frost at Blue 
Mountain Peak, but probably no frost has ever taken place at altitudes 
lower than 6,500 feet (1,980 meters). The open character of the vege- 
tation on the higher peaks and ridges, to be presently described, would 
make possible an amount of radiation sufficient to give a depression as 
great as that observed at Cinchona. 

SOIL TEMPERATURE. 

Readings of the temperature of the soil at a depth of 6 feet were made 
at Cinchona for five years, the apparatus being an ordinary driven 
thermometer in metal casing. The instrument stood in ground covered 
by a sod and was read twice daily, at 7 a. m. and 3 p. in. The mean 
of these readings, when they were not the same, is taken as the daily 
mean and in table 4 are exhibited the monthly means for the years 
1892 to 1896, inclusive. 

Table 4. 



Month. 


Mean 
temp. 


Month. 


Mean 
temp. 


January 

February 

March 

April 


61.4 
60.8 
60.5 
60.4 
60.2 
60.8 


July 

September. . . 

October 

November. . 

December . . 


62.2 
62 . 5 
63.3 
62.9 
62.6 
61.9 


May 


June 





Annual mean 61.6 (16.4 C.) 

Annual mean range .9 (1.5 C.) 



CLIMATOLOGY OF RAIN-FOREST REGION. 



13 



It may be noted that the annual minimum falls in May, three months 
after the minimum for the air; the annual maximum in September, one 
month after that for the air. The correspondence of the annual mean 
temperature of the soil at 6 feet with that of the air to within 1 is here 
confirmed: 61.6 1 = 60.6, as compared with 60.8, the mean of the 
air readings. 

HUMIDITY AND FOG. 

The humidity record for Cinchona consists of daily readings of 
stationary wet and dry bulb thermometers at 7 a. m. and 3 p. m. A 
number of comparisons of wet-bulb readings with sling psychrometer 
readings were made in 1906 and 1909, showing that the wet-bulb readings 
are as a whole from 1.5 to 3 per cent too high, owing to the stationary 
character of the wet -bulb apparatus. Table 5 gives the monthly means 

Table 5. 



Month. Per cent. 


Month. 


Per cent. 


January 84 


Julv 


79.6 
80.4 
84.4 
88.9 
86.0 
86.3 


February 

March 

April 


83.1 
83.9 
83.4 
85.2 


August 

September 

October 

November 

December 

Year 


May 


June 


84.8 




84.1 



for fifteen years (1891 to 1905, inclusive), the mean of the two daily 
readings being taken as the daily mean. The reduction to percentages 
has been made with a table prepared by Mr. \V. Maxwell Hall, and no 
correction for the inherent error of the instrument has been made. 

A general correspondence may be seen, as is to be expected, between 
the annual curve of humidity and that of rainfall (fig. 1). 

The high humidities prevalent at Cinchona and throughout the Blue 
Mountains are due in great part to the high percentage of cloudiness 
and the frequency of fog. On the northern slopes of the range at all 
elevations from below 4,500 feet to the summits of the highest peaks 
fog is prevalent from 10 a. m. to 4 p. m. on a very high percent age of 
the days in all months except February, July, and August. On the 
southern slopes the amount of fog is much less. Fog at night is rather 
exceptional, occurring more often, in my own observation, on the 
summits of the Main Ridge than below 5,800 feel 

RAINFALL. 

The rainfall readings at Cinchona have been mad-' from a Xegretti 
and Zambra gauge of the ordinary type from day to day as the fall 
required. Those at New Haven Gap and Blue Mountain Peak were 
made on the last day of each month, no allowance being made for 



14 



A MONTANE RAIN-FOREST. 



evaporation. Table 6 gives the monthly means of rainfall for tl 
three localities, those for Cinchona being based on records for thirty- 
nine years (1871 to 1909 inclusive); those for New Eaves Gap on 

fourteen years (1882 to 1895, with twenty-four single months missing) ; 
those for Blue Mountain Peak on nineteen years (1890 to 189X, witli 
nine months missing) : 

The data for the three mountain stations show an abundant rain- 
fall at all seasons, but a fall which is not great as compared with 
such localities as Colon, Panama (112.G inches), Kamerun (151.2 



Jan. Feb. Mar. Apr. May Jun. Jul.. Aug. Sept Oct. Nov. Dec 



68' 


TEMPERATURE 61 
60 
59 
58 



88% 

HUMIDITY m 
82 
80 



18 >" 

16 

14 

12 

RAINFALL 10 

8 

6 

4 





NUMBER OF 

RAINY DAYS 



20<taJ 

18 
16 
14 
12 

10 






WIND 



Fig. 1. Annual curves of monthly means of principal elements 
of the climate at Cinchona. 



inches), Sierra Leone (124 inches), and Ratnapura, Ceylon (149.7 
inches). There is a pronouncedly heavier fall in May and in the 
late autumn and early winter months, whereas the lightest falls 
of the midsummer are seldom low enough to cause serious damage 
to other than the most hygrophilous vegetation. At Cinchona the 
annual maximum is reached in October, the minimum in February; at 
New Haven Gap the maximum is in December, the minimum in March; 
at Blue Mountain Peak they are in November and March respectively. 
There is an extreme degree of variability in the rainfall from year to year 



SHREVE 



Plate 4 




CLIMATOLOGY OF RAIN-FOREST REGION. 



15 



and month to month. At Cinchona the highest annual falls were 108.12 
inches in 1877 and 178.77 inches in 1909, the lowest 59.46 inches in 1897. 
In October the fall has been as heavy as 43 inches in 1904 and as light as 
2.67 inches in 1891. In February the fall has been as great as 12.72 
inches in 1893 and as little as 0.83 inch in 1903. The average depar- 
tures from the mean for February and October for thirty-five years are 



Table 6. Monthly mean rainfall for Cinchona, New Haven Gap, and Blue Mountain Peak. 



Cinchona 

New Haven Gap 

Blue Mountain Peak 

Resource (1 mile south of Cinchona, 

elevation 3,700 feet) 

Port Antonio, (sea-level, north coast) 
Kingston (sea-level, south coast) .... 



Jan. 



7. OS 
15.21 
11.96 



Feb. Mar. 



4.01 

7.44 

10.41 



Apr. May 



5.23 6.16 10.68 
7.28 9.13 11.32 
6.57 11.56 14.25 



June. 



8.11 

9.21 

12.77 



July. 



3.80 
5.90 
9.37 



Cinchona 

New H iven Gap 

Blue Mountain Peak 

Resource (1 mile south of Cinchona, 

elevation 3,700 feet) 

Port Antonio (sea-level, north coast) 
Kingston (sea-level, south coast) . . . 



Aug. 



8.04 
4.78 
8.59 



Sept. 



9.73 
6.36 
9.89 



Oct. 



17.91 
20.05 
22.11 



Nov. 



14.29 
15.67 
27.95 



Dec. 



10.66 
24.28 
22.59 



Total. 



Inches. 
105.70 
113.85 
168.02 

67.80 
130.48 

37.96 



Cm. 
268.5. 
2S9.0 
426.8 

171' 2 

331.5 

96.4 



respectively 2.52 inches (for a mean of 4.01) and 9.93 inches (for a 
mean of 17.91). At New Haven Gap during April, May, and June 
1892 there was not a measurable amount of precipitation, while during 
these months in 1894 there were 62.02 inches of rain. 

The number of days per month at Cinchona on which there was a 
fall of 0.01 inch or more is exhibited in table 7, being the means of 
eighteen years (1892 to 1909 inclusive): 



Table 7. Monthly mean number of rainy days. 



Month. 


Days. 


Month. 


Days. 


January 

February 

March 

April 


14.5 
12.3 

12.2 
12.2 

16.1 

12.8 


July 


10.0 
11.4 
16.2 

21 (I 
is. 4 
15.3 




September 

October 

November 

Deccinlii i 

Year 


May 


June 




172.4 



lfi 



A MONTANE RAIN-FOREST. 



There is do other form of precipitation than nun, hail and snow being 

unknown, although the former occurs at rare intervals in the Lowlands. 
The precipitation is either in the form of light Bhowers of brief dural ion 
or prolonged but gentle downpours particularly characteristic of the 

May and winter rainy seasons and not uncommon at night during the 
winter. There is never, so far as I have observed and can learn r the 
hard downpour of large raindrops characteristic of tropical lowlands. 
The frequency of showers too light to register 0.01 inch is high, and 
they are not without influence on the vegetation. Although the number 
of rainy days is great and the frequency of light showers is high, yet 
the bulk of the annual rainfall is registered during the prolonged 
downpours. In the 168 months of 1892 to 1905 inclusive, there were 
23 (14 per cent) in which 50 per cent or more of the monthly total fell 
upon one day; 64 (38 per cent) in which it fell upon two days; 45 
(27 per cent) in which it fell upon three; and 36 (21 per cent) remaining 
in which it was more evenly distributed. The heaviest single daily 
falls of rain at Cinchona were 28.66 inches on May 25, 1898; 11.50 
inches on August 10, 1903 (accompanying the hurricane which visited 
the island on that date), and 18.30 inches on November 8, 1909. 

Dew is formed abundantly in open situations on clear nights at all 
seasons of the year. 



SUNSHINE AND CLOUDINESS. 

No indication of the relative amounts of sunshine and cloudiness 
is given by the figures exhibiting the number of rainy days, owing to 
the high frequency of foggy or cloudy days on which there is not an 
appreciable amount of precipitation. No records of sunshine have 
been kept at Cinchona by the Department of Public Gardens and 
Plantations. From November 1905 to March 1906 I kept a rough 
record of the number of hours of sunshine by observing the time at 
which it clouded over every day, and by estimation of the number of 
hours of sun during the part of the day when it is intermittently cloudy. 
My figures are shown in table 8, expressed in percentages of the total 
possible hours of sunshine. 

Table 8. Average percentage of sunshine, Not. 1905 to Mar. 1906. 



Month. 


Per cent. 


November 

December 

January 


28 
16 
21 
29 

27 

24 


February 

March 


Mean 



SHREVE 



Plate 5 




CLIMATOLOGY OF RAIN-FOREST REGION. 



17 



During these months the number of totally clear days was 6, the 
number of totally cloudy or rainy days was 50, the number of partially 
cloudy days 95. The total rainfall for these five months was 37.07 
inches as contrasted with the mean of 41.27, while the number of rainy 
days was 74, the mean number being 72.7. This is partial, if not 
absolutely conclusive evidence that the above percentages are not 
below the normal. 

The typical course of the day's weather is: clear from sunrise until 
9 to 11 a. m., intermittently or entirely cloudy until nearly sunset, 
with two to three hours of fog in the mid-day or early afternoon, the 
sun setting clear. Rain usually occurs in the mid-day or early after- 
noon and the night is clear. During the summer months the percent- 
age of sunshine is much greater than in the months tabulated above, 
but is so intermittent that it would be impossible to determine its 
percentage of the total number of hours without the use of appropriate 
instruments. 

WIND. 

The wind at Cinchona is prevailingly from the east and northeast 
and commonly reaches its highest force at night and in the winter 
season. Its influence on the vegetation is greatest on the peaks and 
ridges, and the fact that the lowest humidities accompany high wind 
may make its desiccating influence considerable. The monthly mean 
velocities of the wind in miles per day at Cinchona for eight years (1892 
to 1899 inclusive), as measured by a Negretti and Zambra anemom- 
eter, are shown in table 9. The annual curve shows little save the 
lower rate in the rainy months (fig. 1). 

Table 9. Monthly mean wind velocity. 



Month. 


Velocity. 


Month. 


Velocity. 


February 

March 

April 


38.1 
39.2 
36.2 
23 . 2 
18.1 
36.8 


July 


37.7 
29.4 
is. 4 
27.4 
40.6 
49.0 


August 

September 

October 

November 


May 


June 





The annual mean daily velocity: 32.8 miles per day. 



THE FLORA OF THE RAIN-FOREST. 

Throughout the long history of the botanical exploration of Jamaica 
the flora of the Blue Mountains has received attention from numerous 
collectors, as well as from several systematists who have never visited 
the island. Among the earlier students were Swartz, Browne, Jacquin, 
Macfadyen, Purdie, M'Nab, Prior, and Marsh. More recently the 
activity of the Department of Public Gardens and Plantations, for a 
number of years located at Cinchona, in cooperation with the botanical 
gardens at New York and Berlin, has added considerably to a knowl- 
edge of the flora. At the present time these mountains may be looked 
upon as botanically well known, except in their less accessible parts to 
the north and northeast of Blue Mountain Peak. 

The only comprehensive systematic work available for the Blue 
Mountain area is Grisebach's Flora of the British West Indies (1864). 
Since its appearance a number of new species from the region have been 
described in the Symbolae Antillanae, by Urban and his co-workers, 
and in the Bulletin of the Torrey Botanical Club by Britton. For the 
ferns an excellent manual exists in Jenman's Synoptical List of the 
Ferns and Fern-Allies of Jamaica, 1 since the publication of which a 
number of new fern species have been described from the region by 
Underwood and by Maxon. I have depended for my knowledge of 
the flora on the above-mentioned works, and on the determinations of 
my own collections, which have been made in part by Dr. N. L. Britton 
and Mr. W. Ralph Maxon, to whom most grateful thanks for this 
service are here returned, and in part by Mr. William Harris, who 
possesses more complete first-hand knowledge of the region than any 
other botanist. 

I have not been concerned with a complete listing of the flora, but 
have endeavored to secure accurate determinations of all species which 
go to make up the characteristic features of the vegetation. In order 
to bring together in taxonomic sequence, with author names, all the 
plants mentioned in the description of the vegetation, the following 
list is given. The sequence is that of the Natiirlichen Pflanzenfamilien ; 
the nomenclature for Pteridophytes is in accordance with Christensen's 
Index Filicum, and the names for the Phanerogams have been brought 
into agreement with the Vienna code through the kindness of Dr. 
I. Urban. In the Pteridophytes the synonyms given in parentheses 
are those used in Jenman's List ; in the Phanerogams those of the Dames 
occurring in Grisebach's Flora and Fawcett's List which are now obso- 
lete have been given as synonyms, to which are added some names of 
extra-Jamaican forms, to which the Jamaican species were erroneously 
referred by early workers. 

'Jenman, Synoptical List cf the Ferns and Fern Allies, ifull. Dept. Pub. Gardens and Plant. 
Jamaica. 

18 



SHREVE 



Plate 6 




a 



x 



THE FLORA OF THE RAIN-FOREST. 



19 



List of Characteristic Species. 



PTERIDOPHYTA. 

Hymenophyllacese. 

Trichomanes reptans Sw. 

Trichomanes hookeri Presl. (Trichomanes 
muscoides Sw.) 

Trichomanes crispum L. 

Trichomanes pyxidiferum L. 

Trichomanes capillaceum L. (Tricho- 
manes trichoideum Sw.) 

Trichomanes scandens L. 

Trichomanes radicans Sw. 

Trichomanes rigidum Sw. 

Hymenophyllum tunbrigense (L.) Sm. 

Hymenophyllum fucoides Sw. 

Hymenophyllum polyanthos Sw. 

Hymenophyllum axillare Sw. 

Hymenophyllum crispum H. B. K. 

Hymenophyllum hirsutum (L.) Sw. 

Hymenophyllum sericeum Sw. 

Cyatheacese. 

Balantium coniifolium (Hook.) J. Sm. 

(Dicksonia coniifolia.) 
Cyathea pubescens Mett. 
Cyathea tussacii Desv. 
Cyathea insignis Eaton. 
Cyathea harrisii Underw. 
Cyathea furfuracea Bak. 
Alsophila ciuadripinnata (Gmel.) C. Chr. 

(Alsophila pruinata Kaulf.) 

Polypodiacese. 

Dryopteris hirta (Sw.) O. Kze. (N'eph- 

rodium hirtum Hook.) 
Dryopteris effusa (Sw.) Urban. (Nephro- 

dium effusum Bak.) 
Polystichum plashnickianum (Kze.) Moore. 
Polystichum struthionis Maxon. 
Polystichum denticulatum (Sw.) J. Sm. 
Nephrolepis cordifolia (L.) Presl. 
Odontosorea aculeata (L.) J.Sm. (Daval- 

lia aculeata Sw.) 
Dennstcedtia dissecta (Sw.) Moore (Dick- 
sonia dissccta Sw.) 
Diplazium celtidifolium Kze. (Asplenium 

ccltidifolium Webb.) 
Diplazium costale (Sw.) Presl (Asplenium 

costale Sw.) 
Diplazium altissimum (Jenm.) C. Chr. 

(Asplenium altissimum Jenm.) 
Diplazium brunneo-viride (Jenm.) C. Chr. 

I Asplenium brunneo-viride Jenm.) 
Asplenium resiliens Kze. 
Asplenium obtusifolium L. 
Asplenium pteropus Kaulf. 

Asplenium alatum II. B. Willd. 

Asplenium lunularum Sw. 

Asplenium dimidiatum Sw. 

Asplenium eristatum Lam. (Asplenium 

cicutarium Sw.) 
Plagiogyria biserrata Webb. 
Blechnum attenuatum (Sw.) Mett. (Lo- 

maria attenuate Willd.) 
Blechnum capense (L.) Schl. (Lomaria 

procera Spreng.) 



PTERIDOPHYTA Continue 1. 

Polypodiacese Continued . 

Blechnum tabulare (Thunb.) Kuhn. (Lo- 
maria boryana Willd.) 
Blechnum occidentale L. 
Ceropteris tartarea (Cav.) Link. (Gym- 

nogramme tartarea Desv.) 
Cheilanthes microphylla Sw. 
Hypolepis nigrescens Hook. 
Hypolepis pulcherrima Underw. & Maxon. 
Pteris longifolia L. 
Pteris podophylla Sw. 
Pteris deflexa Link. 
Histiopteris incisa (Thunb.) J. Sm. (Pteris 

incisa Thunb. 
Pteridium aquilinum (L.) Kuhn. (Pteris 

aquilina L.) 
Paesia viscosa St. Hil. (Pteris viscosa 

Moore) . 
Vittaria lineata (L.) Sm. 
Antrophyum lineatum (Sw.) Kaulf. 
Polypodium serrulatum (Sw.) Mett. 

(Xiphopteris serrulata Kaulf.) 
Polypodium myosuroides Sw. (Xiphop- 
teris myosuroides.) 
Polypodium gramineum Sw. 
Polypodium marginellum Sw. 
Polj'podium grisebachii L'nderw. (Poly- 
podium exiguum Griseb.) 
Polypodium basiattenuatum Jenm. 
Polypodium induens Maxon. 
Polypodium cultratum Willd. 
Polypodium suspensum L. 
Polypodium taxifolium L. 
Polypodium plumula H. B. Willd. 
Polypodium polypodioides (L.) Hitch. 

(Polypodium incanum Sw.) 
Polypodium thyssanolepis A. Br. 
Polypodium loriceum L. 
Polypodium crassi folium L. 
Polypodium repens Aublet. 
Polypodium lanceolatum L. 
Elaphoglossum ina;qualifolium (Jenm.) C. 

Chr. (Acrostichum insequalifolium 

Jenm.) 
Elaphoglossum pallidum (Bak.) C. Chr. 

(Acrostichum pallidum Bak.) 
Elaphoglossum latifolium (Sw.) J. Sm. 

(Acrostichum latifolium Sw.) 
Elaphaglossum petiolatuin (.Sw.) l'r!>. 

(Acrostichum viscosum Sw.) 
Elaphoglossum cinchonas Underw. 
Elaphoglossum hirtum (Sw.) C. Chr. 

(Acrostiohum squamosum 8w.) 

Elaphoglossum villosum iSw.) J. Sin. 
(Acrostichum villosum Sw.) 
( ileicheniaceae. 

( ileichenia jamaicenafo (Underw.) 

( ileichenia bancroftii Hook. 

Gleichenia pectinata (Willd.) PteaL 
Marattiaceee. 

Maratlia alata Sw. 

I )aiKra alata Sm. 

Dansea jamaicensLa Underw. 



20 



A MONTANE RAIX-FOREST 



List qf Characteristic Species Continued. 
PTERIDOPHYTA Continued. ANGN 18PERM E Continued. 



ipodiaoeB. 

Lycopodium reflexum Lam. 
Lyoopodium taxifolium 8w. 
Lycopodium cernuura L. 
Lycopodium elavatuxn L. 
Lyoopodium fawcettii Lloyd and Underw. 
(Lycopodium complanatum L.) 

CYMXOSPERM.L. 
TazacecB. 

Podocarpus urbanii Pilfer (Podocarpus 
coriaceus Rich.) 
Pinaceae. 

Juniperus barbadensis L. 

ANGIOSPERALE. 

Graminese. 

Panicum glutinosum Sw. 

Olyria latifolia L. 

Danthonia shrevei Britton. 

Zeugites americana Willd. 

Chusquea abietifolia Griseb. 
Cyperacese. 

Rynchospora eggersiana Boeckl. (Ryn- 
chospora florida Griseb.) 

Rynchospora elongata Boeckl. 

Rynchospora polyphylla Vahl. 

Uncinia hamata (Sw.) Urb. (Uncinia 
jamaicensis Pers.) 
Araceae. 

Anthurium scandens (Aubl.) Engl. 
Bromeliaceae. 

Tillandsia incurva Griseb. 

Tillandsia complanata Benth. 

Caraguata sintenesii Bak. 
Liliaceae. 

Smilax celastroides Kunth. 
Orchidaceae. 

Pleurothallis sp. 

SteUs ophioglossoides (Jacq.) Sw. 

Lepanthes tridentata Sw. 

Lepanthes concinna Sw 

Lepanthes concolor Fawc. and Rendle. 

Liparis elata Lindl. 

Calanthe mexicana Reichenb. f. 

Isochilus linearis (Jacq.) R. Br. 

Epidendrum cochleatum L. 

Epidendrum ramosum Jacq. 

Epidendrum verrucosum Sw. 

Dichaea trichocarpa Lindl. 

Dichaea graminea (Sw.) Griseb. 

Dichaea glauca Lindl. 

Spiranthes elata (Sw.) L. C. Rich. 

Physurus plantagineus (L.) Lindl. 

Physurus hirtellus (Sw.) Lindl. 

Prescottia stachyodes Lindl. 
Piperaceae. 

Piper geniculatum Sw. 

Piper fadyenii C. DC. 

Piper tuberculatum Jacq. 

Peperomia hispidula (Sw.) A. Dietr. 

Peperomia tenella A. Dietr. 

Peperomia glabella A. Dietr. 

Peperomia basellaefolia Kunth. 



PiperacesB < Continued. 

Peperomia "lt usifolia mr. 
P( peromia galioidee Kunth. 

Pep<Tomia filiformis A. Dietr. 

Peperomia verticUlata (L.) A. Dietr. 
Peperomia refleza (L. f.) A. Dietr. 

I'cpcrniiiia turf(/~a ( '. D' '. 

Peperomia rupigaudens ( '. DC. 
Chloranthaces. 

Hedyosmum nutans Sw. 

Hedyosmum arboreBcens Sw. 
Myricaceee. 

Myrica microcarpa Benth 
Urticaceie. 

Pilea micropbylla (L.) Liebm. 

Pilea parietaria (L.) Blume. 

Pilea parietaria var. alpe-tris I'rb. 

Pilea grandifolia (L.) Blume. 

Pilea nigrescens Urb. 

Pilea brittonise Urb. 

Boshmeria caudata Sw. 

Phenax hirtus (Sw.) Wedd. 
Loranthaceae. 

Loranthus parvifolius Sw. 

Phthirusa lepidobotrj-s (Griseb.) Eicbi. 
(Loranthus lepidobotrys Griseb.) 

Dendrophthora cupressoides (Griseb.) 
Eichl. (Arceuthobium cupressoides 
Griseb.) 

Dendrophthora gracilis (Griseb.) Eichl. 
(Arceuthobium gracile Griseb.) 

Dendrophthora danceri Kr. and Urb. 

Phoradendron Havens Griseb. 

Eubrachion ambiguum var. jamaicense Kr. 
and Urb. 
Amarantaceae. 

Iresine celosioides L. 
Lauraceae. 

Nectandra coriacea (Sw.) Griseb. 

Nectandra patens (Sw.) Griseb. 
Papaveraceae. 

Bocconia frutescens L. 
Cunoniacea?. 

Weinmannia pinnata L. (Weinmannia 
glabra L. f., Weinmannia hirta Sw.) 
Rosacea?. 

Rubus alpinus Macf. 

Fragaria vesca L. 
Rutaceae. 

Fagara hartii Kr. and Urb. 
Simarubaceae. 

Brunelha comocladifolia Humb and Bonpl. 
Meliaceae. 

Guarea swartzii DC. (Guarea trichili- 
oides L.) 
Euphorbiaceae. 

Acalypha ^gata L. 

Alchornea latifolia Sw. 

Mettenia globosa (Sw.) Griseb. 

Cyrillaceae. 

Cyrilla racemiflora L. (Cyrilla antillana 
Michx.) 



THE FLORA OF THE RAIX-FOREST. 



21 



List of Characteristic Species Continued. 



ANGIOSPERMJE Continued. 

Aquifoliaccae. 

Ilex montana var. occidentalis Loes. 

Ilex obcordata Sw. 
Sapindaceae. 

Turpinia occidentalis Don. 

Dodonaea angustifolia Sw. (Dodonaea 
viscosa L.) 
Rhamnaceae. 

Rhamnus sphaerospermus Sw. (Frangula 
sphaerocarpa Griseb.) 
Malvaceae. 

Malvaviscus arboreus Cav. 
Marcgraviaceae. 

Maregravia brownei Urb. 
Theaceae. 

Cleyera theoides (Sw.) Choisy. 

Haemocharis haematoxylon (Sw.) Choisy. 
(Laplacea haematoxylon Camb.) 

Haemocharis villosa (Macf.) Choisy. (Lap- 
lacea villosa Griseb.) 
Guttiferae. 

Clusia havetioides PI. and Triana. (Tovo- 
inita havetioides Griseb.) 
Hypericaceae. 

Ascyrum hyperieoides L. 
Bixaceae. 

Xylosma nitidum (Hell.) A. Gray. (Myr- 
oxylon nitidum (Hell.) Kuntze.) 
Passifloraceae. 

Passiflora sexnora Juss. 

Passiflora penduhflora Berter. 
Begoniaceae. 

Begonia nitida Dryand. 

Begonia acuminata Dryand. (Begonia 
jamaicensis A. DC.) 

Begonia scandens Sw. 
Thymeleaceae. 

Daphnopsis tinifolia (Sw.) Griseb. 
Myrtaceae. 

Eugenia fragrans (Sw.) Willd. (Myrtus 
fragrans Sw.) 

Eugenia alpina (Sw.) Willd. 

Eugenia marchiana Griseb. 

Eugenia biflora var. wallenii Kr. and Urb. 

Eugenia harrisii Kr. and Urb. 

Psidium montanum Sw. 
Melastomaceae. 

Meriania purpurea Sw. 

Meriania leucantha Sw. 

Miconia quadrangularis (Sw.) Naud. 

Miconia rubens (Sw.) Naud. (Tamonea 
rubens Sw.) 

Miconia rigida (Sw.) Triana. (Tamonea 
rigida Sw.) 

Heterotrichum patens (Sw.) DC. 

Mecranium purpurascens (Sw.) Triana. 

Blakea trinervis L. 
Araliaec;r. 

Sciadophyllum brownei Spreng. 

Gilibertia pendula (Sw.) E. March. (Den- 
dropanax pendula Decne. and Planch. 

Gilibertia nutans (Sw.) E. March. (Den- 
dropanax nutans Sw.) 

Gilibertia arborea (L.) E. March. (Dendro- 
panax arboreum Decne. and Planch.) 



ANGIOSPERM.E Continued. 

Araliaceae Continued. 

Oreopanax capitatum (Jacq.) Decne. and 
Planch. 
Umbelliferae. 

Hydrocotyle pusilla Rich. 
Cornaceae. 

Garrya fadyenii Hook. 
Clethraceae. 

Clethra alexandri Griseb. 

Clethra occidentalis (L.) Steud. (Clethra 
tinifolia Sw.) 
Vacciniaceae. 

Vaccinium meridionale Sw. 
Ericaceae. 

Lyoiria jamaicensis (Sw.) Don. 

Lyonia octandra (Sw.) Griseb. 
Myrsinaceae. 

Rapanea ferruginea (R. & P.) Mez (Myr- 
sine laeta A. DC.) 

Wallenia venosa Griseb. 

Wallenia crassifolia Mez. 

Wallenia fawcettii Mez. 
Sapotaceae. 

Dipholis montana (Sw.) Griseb. 
Gentianaceae. 

Lisianthus latifolius Sw. (Leianthus^lati- 
fohus Griseb.) 
Asclepiadaceae. 

Metastelma fawcettii Schlecht. 

Metastelma atrorubens Schlecht. 

Metastelma ephcdroides Schlecht. 
Convolvulaceae. 

Ipomcea triloba L. 
Borraginaceae. 

Tournefortia cymosa L. 
Verbenaceae. 

Lantana camara L. 

Citharexylum caudatum L. 
Labia tae. 

Micromeria obovata (W.) Benth. 

Salvia jamaicansis Fawc. 
Solanaceae. 

Solanum punctulatum Dun. 

Acnistus arborescens (L.) Schlecht. 

Datura suaveolens Hunib. and Bonpl. 

Cestrum hirtum Sw. 

Cestrum sp. 

Brunfelsia jamaicensis (Benth.) Griseb. 

Brunfelsia harrisii Urb. 

Solandra grandiflora Sw. 
Gesneraceae. 

Gesnera inimuloides (Griseb.) Urb. 

Columnea hirsuta Sw. 

Beshria lutea L. 
Rubiacea\ 

Manettia lygistum Sw. 

Paychotria brownei Sprong. 
Psychotria corymbosa Sw. 
I'.ilicourca crocea (Sw.) It. iV; B. 
Relbunium hypooarpium (L.) Hcmsl. 
(Galium hypocarpium Endl.) 
Caprifoliacea). 

X'il'urnui.i VUloSUID Sw. 

Viburnum alpinum Macf. (Viburnum 

glabratum H. B. K.). 



22 



A MONTANE RAIN-FOREST. 



List of Characteristic Specie) Continue I. 



ANGIOSPERMjE Continued. 

i 'uourhitaoeB. 

Cionomoye pomiformu [Macf.) <;ri-rl>. 
Campanulaoeas. 

Lobelia martagoo (< rriseb.) Hitch. (Tupa 

martagoo ( rriseb.) 
Lobelia aasurgens L. (Tupa aasurgens 

I .) DC.) 
Lobelia caudata (Griseb.) Urban. (Tupa 
oaudata (iriseb.) 
(*uni|io.-i 

Vernonia divaricata Sw. 
Vernonia intonsa (Jleason. 
Vernonia arboreacens Sw. 
Eupatorium dalea (L.) DC. 



INGIOSPERM i: -< lontinued. 

i oxnpositffl i lontinued. 

Eupatorium eritonifonne Urb. 
Kupatoriuni parviflorum Bw. 
Eupatorium Luoidum < )rt. 
Eupatorium corylifolium Griseb. 

Ilarcliaris scoparia Sw. 

Bidens ooreopsidia DC. 
Bidena shrevei Britton. 
Liabum umbcllatum (L.) Sen. Bip. I .. i- 

Imra brownei Cass.) 
Si-iiccio swartzii DC. 
Senecio fadyenii Griseb. 
Seneeio Iaciuiatus (Sw.) DC. 



THE VEGETATION OF THE RAIN-FOREST. 
ECOLOGICAL CHARACTERISTICS OF THE RAIN-FOREST. 

The peaks and highly-eroded slopes of the Blue Mountains, in the 
absence of cliffs and rock outcrops of any considerable size, and in the 
lack of any disturbance by man, exhibit a forest covering of striking 
continuity. (See upper slopes of range in plate 5). The color tone 
of the landscape is a dull mingling of darker shades of green, with a 
blending of gray on the ridges, where Usnea is common in the open 
tree tops. Neither among the forest trees nor the smaller constituents 
of the vegetation are there any conspicuous colors of leaf or flower. 
Clethra occidentalis occurs in sufficient abundance for its racemes of 
white flowers to be a somewhat noticeable feature of the autumn land- 
scape, and at the same season the large yellow flowers of Bidens shrevei 
cover the crown of trees into which it has climbed, and touches of red 
are here and there given the forest by the autumn coloration of the 
two species of Alburnum. The only other showy bloomers of the 
arboreal flora are Hcemocharis hcematoxylon and Meriania purpurea. 
In the former the flowers are white and in the latter a deep red, and 
when the two are in bloom simultaneously in the spring they give a 
touch of color to the otherwise dull landscape. In the interior of the 
heaviest rain-forest there is an almost utter absence of colors other 
than green, which with the absence of showy birds and insects gives 
the forest an air of gloom to which its continual fogginess only adds. 

There are no gigantic trees towering above the general level of the 
forest, and indeed the stature of the trees is surprisingly small in view 
of the apparent favorableness of the rainfall and temperature condi- 
tions. In ravines they may attain to a height of 60 feet, but on the 
ridges, particularly those at high altitude, the largest individuals of 
Podocarpus and Clethra seldom exceed 20 feet in height. The combined 
influences of wind and occasional low water content of the soil may 
contribute to the low stature of the trees of the ridges at higher alti- 
tudes, but in general the phenomenon is due to the rapidity of erosion. 



VEGETATION OF THE RAIN-FOREST. 23 

Nearly all the trees on slopes, even many young ones, show a leaning 
down hill (see plate 12), larger ones are often bent over nearly to the 
horizontal, while the number of down-fallen trunks, all pointing down 
hill, indicates only too clearly the destructive influence of erosion on 
the older trees. Only along the beds of valleys where the soil is rela- 
tively stable have I seen trees of more than 30 inches (76 cm.) trunk 
diameter, these usually being Solarium punctulatum or Gilibertia arborea. 

The forests of the Blue Mountains exhibit an intermingling of tem- 
perate and tropical characteristics both in their composition and their 
general ecology. I made no exact determinations of the composition 
of the forest because of the impossibility of securing satisfactory data 
where the rapidity of erosion causes so many complications in the forest 
stand. However, rough estimations which I made in a number of 
localities indicated that Clethra occidentalis, Vaccinium meridionale, and 
Podocarpus urbanii form about 50 per cent of the stand and that an 
additional 35 per cent is made up of some 10 other species, as follows : 
Alchornea latifolia, Cyrilla racemiflora, Ilex montana var. occidentalis, 
Guarea swartzii, BruneUia comocladifolia, Clusia havetioides, Gilibertia 
arborea, Rapanea ferruginea, Solarium punctulatum, and Eugenia biflora 
var. wallennii. In other words, the general character of the composi- 
tion is that of temperate forests rather than of those in tropical lowland-. 
The examinations which I have made of virgin lowland forests in the 
valley of the Mabess River in the northeastern part of Jamaica and in 
the vicinity of Mount Diablo, in the central part, make me quite 
confident in stating that they are far more complex in their composition 
than the mountain forests and more so than the forests of the Philippine 
Islands which have been described by Whit ford. 1 The constant 
overturning of the largest trees by erosion gives opportunity for the 
entrance of young individuals, and results in a great diversity in trunk 
diameters. Clethra, Vaccinium, and Podocarpus all sucker freely from 
old roots and trunks, so that a single root system often anchors a thick 
horizontal trunk and several young vertical ones, which adds still 
further to this diversity. 

The individual trees are mostly of temperate rather than of tropical 
type in the order of branching and shape of the crown. In Vaccinium, 
Podocarpus, Clethra, Ilex, and other common forms the order of branch- 
ing varies from the seventh to the ninth, or is even higher; in BruneUia 
comocladifolia alone is there a low order the fourth. In Rapanea 
ferruginea the lateral branches exceed the main trunk in growth; in 
BruneUia there is a lax, open crown, and in Eugenia fragrans and 
Eugenia alpina there are round compact heads of foliage With these 
exceptions there are no trees which present any peculiarities of form. 
The bark is universally smooth and thin. Cauliflory 1<<^ not occur. 

1 Whitford, H. N. The Vegetation of the I.amao I'm.'- Reserve. Philip. Jour. S, i . I. 
373 431. G37-G82. 1906. 



24 A MONTANE RAIN-FOREST. 

l>ut is simulated in several species in which the flown- are produced 

from the axils of the fallen leaves of the preceding year, as in EuQi nm 

marchiana, Acnistus arborescent, Mecranium purpuraecens, and Alchor- 

iK a ladfolia. Such purely tropical characteristic- as plank butt re 

and the hunching of leaves at the ends of the branches are entirely absent. 

The attenuated leaf ends or "dripping points" which have been 
found to characterize the rain-forests of the eastern hemisphere, are 
very uncommon in the Jamaican rain-forest, and the functional value 
of such structures appears to have been overestimated. 1 

Only in the narrowest ravines is there a lofty and closed canopy, and 
as one proceeds into wider ravines and from them onto slopes and 
finally onto the ridges the canopy becomes more and more open, 
although its general level is more uniform on the ridges than in the 
ravines. The canopy itself has no line of demarcation from the foliage 
of the under-trees and shrubs, resulting in an irregular and more or 
less solid mass of foliage from the tree tops down nearly to the level 
of the terrestrial herbaceous plants. There is, however, just above the 
herbaceous vegetation a layer free of foliage, which in wide ravines 
sometimes reaches as high as 10 or 20 feet (3 to 6 meters), but on the 
slopes and ridges disappears altogether. 

The leaves of the generality of trees and shrubs are of medium or 
small size, from about 75 sq. cm. in area in Clethra alexandri to less than 
1 sq. cm. in Eugenia alpina (see plate 21 A). In all but three of the 
commonest trees (Brunellia, Weinmannia, and Guarea) the leaves are 
simple, and without exception they are firm or even coriaceous, with 
from one to four layers of greatly elongated palisade cells and with 
compact mesenchyma, in high contrast to the extremeh' hygrophilous 
character of the leaves of the ferns and other herbaceous plants of the 
forest floor. 

The floor of the rain-forest is covered with a litter of leaves, twigs, 
and limbs, the decay of which seems to be retarded rather than accel- 
erated by the extreme wetness maintained at relatively low tempera- 
tures. Ants do a small amount of work in destroying dead trees 
before they fall, and an abundance of small discomycetous fungi 
(almost the only representatives of their group) hastens the disinte- 
gration of the leaves and small twigs. The soil is extremely rich in 
organic matter, but is shallow and full of angular rock fragments. 

The terrestrial herbaceous vegetation varies from extreme wealth 
in the ravines to almost complete absence in many places on the ridges 
where the climbing bamboo, Chusquea abietifolia, is abundant, and 
where the amount of light reaching the forest floor is so great as to 
permit the development of extended thickets of the scrambling ferns 
Gleichenia and Odontosorea. In the ravines ferns form by far the most 

^hreve, Forrest, The Direct Effects of Rainfall on Hygrophilous Vegetation. Jour, of 
Ecology, 2, 1914. 



SHREVE 



Plate 7 




\ Windward Ravine enveloped in the usual mid-day lot. The shrubs are species of Piper and Boehtnerui; 
the tree-fern is Cyathea insignis; .- 1 u i i 1 1 ~ t the sky hang festoons of the climber Ma cq avia brown 



1 



VEGETATION OF THE RAIN-FOREST. 25 

prominent part of the herbaceous vegetation, with species of Pilea 
and Peperomia in the minority and terrestrial orchids not abundant. 
Species of Rynchospora and the endemic sedge Uncinia hamata are not 
infrequent in more open situations, but the sedge and grass types are 
uncommon on the whole, as are also monocotyledonous plants in 
general. The absence of palms and of the musaceous type of large- 
leaved phanerogams in general, taken together with the presence of 
tree-ferns and filmy ferns and the general predominance of bryophytes 
and pteridophytes, marks the salient features of this type of rain-forest. 

In the abundance of its epiphytic vegetation the rain-forest is trop- 
ical in character. Tank epiphytes of the bromeliaceous type are com- 
mon, although represented by but few species; large woody forms are 
not frequent. Orchids, with either water-storing leaves or storing 
roots, are common, but are not so frequent as the ferns, which range 
from large hygrophilous forms to small xerophilous ones, including 
notably a number of species of Hymenophyllaceae. A large part of 
the bulk of the epiphytic vegetation is made up of mosses and hepatics, 
which serve as a water-retaining substratum for the larger forms. 

The representation of lianes is poor, particularly outside the ravines, 
where Marcgravia and several asclepiadaceous forms occur together 
with the low-growing climbing ferns, species of Poly podium and Blech- 
num. The scrambler Chusquea is abundant in the open forest of slopes 
and ridges. 

The continuity of the forest formation is broken by occasional land- 
slips and by the thickets of scrambling ferns along the ridges and on 
the highest peaks. On the northwestern face of Sir John Peak, near 
its summit, and on the same face of Mossman's Peak are also patches 
of a coarse bunch-grass (Danthonia shrevei), which has not been col- 
lected elsewhere in the island. It grows in large hummocks (see plate 
19), and is accompanied by scattering plants of Gleichenia , with dwarf 
individuals of Clethra alexandri, Ilex obcordata, and Weitwiannia 
pinnata about the edges. The areas are not old landslips, the char- 
acter of their soil is not peculiar, neither are they exposed to conditions 
any more adverse to tree growth than those operative on the peaks 
themselves. It is impossible to gain any notion whether the areas are 
encroaching on the forest. The habit of the grass is such as to cover 
and completely shade the ground, and seedlings of other plants are 
rare between the hummocks. The rapidity of the erosion now going 
on makes it highly probable that in recent geological time the Blue 
Mountains extended considerably above their present altitude. At a 
time when these two peaks were loftier they would, in all probability, 
have borne alpine grassland above the tree limit, such as Volkens 3 
encountered on Kilimandjaro at 7,800 feet, less than 400 feet higher 
than the summit of Blue Mountain Peak, and at 15 lower latitude. 

Volkens, G., Dir Kiliiunndscharo. Bcrlio, 1897. 



26 A MONTANE RAIN-FOREST. 

These considerations lead mo to the surmise that the patches of Dan- 
thonia on Sir John Peak and Mossman's Peak are relicts of a former 
extensive alpine grassland formation which has been encroached upon 
by the forest as the mountains have l>oen worn down below the tree 
limit. 

HABITAT DISTINCTIONS IN THE RAIN-FOREST. 

An examination of the forest formation which clothes the Blue 
Mountain range reveals both vegetative and floristic differences in 
its character in different localities. These differences are due (1) to 
the climatic difference between the northern, or windward, and the 
southern, or leeward, slopes of the range, which has its basis in differ- 
ences in precipitation and the number of hours of fog and sunshine; 
(2) to local differences due to the highly dissected erosion topography, 
which have their basis in differences of atmospheric humidity and wind 
action; (3) to the altitude, which has its basis partly in temperature 
differences. The marked climatic difference between the northern 
and southern slopes, due to the prevailing direction of the trade wind, 
operates in a manner and direction such as to obscure any influence 
which the direction of slope in relation to insolation might have in 
differentiating the conditions for vegetation on the north and south 
slopes of the range. The low latitude of Jamaica makes this a factor 
which would not be operative in any case for more than a few months 
in winter. In like manner the striking difference in conditions of 
atmospheric humidity between the bottoms of ravines and the summits 
of ridges tends to obscure any influence which differences in amount 
of soil moisture might have in these habitats during the relatively dry 
periods which occasionally supervene. In view r of the excellent dis- 
tribution of the rainfall I feel confident in stating that the fluctuating 
amounts of soil moisture are a negligible factor in the distribution of 
vegetation. During the very exceptional dry periods, such as that 
which has been mentioned as occurring at New Haven Gap in April, 
May, and June, 1892, the depression of soil-moisture content would 
no doubt be sufficient to defoliate, if not to kill, the most hygrophilous 
shrubs and herbaceous plants, particularly as such a rainless period 
would be one of high percentage of insolation, high temperatures, and 
low humidity. 

The differences in temperature which exist between sea-level and 
4,500 feet are profoundly significant to vegetation. The Smaller differ- 
ence which exists betw r een the 4,500 feet (1,372 meters) level and the 
summits of the three highest peaks is of no such importance, although 
it appears to be responsible for the limiting of the vertical distribution 
of many species. During the day the uniformity of moisture conditions 
on the w r indward slopes from 4,500 to 7,400 feet (2,250 meters) tends 
to offset the most important of the temperature influences, that is, on 



SHREVE 



Plate 8 




[nterior "i forest al New Haven ( i:i|> which is identical with thai in Windward Ra> ines. The pendanl 

moss is Phyllogonium fulgens; the t-litiil >iii>_r fern, Blechnum attenualum; the 

large-leaved shrub, Boehmeria caudata. 



VEGETATION OF THE RAIN-FOREST. 27 

transpiration and growth. Indeed, the temperature conditions on the 
windward slope between the altitudes mentioned are made more uni- 
form than on the leeward slope by the fact that much of the dynamic 
cooling of the air driven up from the near-by coast goes into the con- 
densation of moisture. The differences of altitude that exist within 
our area are accompanied by negligible differences in rainfall and cloudi- 
ness. The leeward slopes, however, get a somewhat higher rainfall just 
below the Alain Ridge than at lower altitudes, which is true no matter 
at what altitude on the Main Ridge, and is merely due to precipitation 
from clouds which are carried beyond the crest of the ridge by wind. 

The sets of factors indicated do not operate independently, neither 
do the different habitats fail to shade into one another in the character 
of their vegetation. Deep ravines on the leeward slope resemble in 
many respects less deep ones on the windward side; peaks and ridges 
at lower altitudes resemble those at higher altitudes; ridges which are 
at the same time gaps resemble ravines more than they do the more 
exposed ridges. The ravines vary in width and depth, according to 
their age; when followed upward they broaden and emerge into the 
upper slope of the valley to which they are tributary. 

The ravines and valley bottoms and their adjacent slopes will be 
shown to be the most hygrophilous habitats in the rain-forest; particu- 
larly on the windward slope they show a wealth and luxuriance which 
rival that of the lowland forests, together with the predominance of 
bryophytes and pteridophytes, which is the strongest characteristic of 
the region. 

The following sections embrace a brief descriptive account of the 
vegetation of the Blue Mountain region. The habitats under which 
the descriptions are grouped have been distinguished in accordance 
with the conditions just discussed. The most important distinction 
within the region is that between the two slopes of the range, which 
are designated the Windward and Leeward rather than the Northern 
and Southern, in order to emphasize the fact that it is the climatic 
difference between them due to the trade wind and not the chance fact 
of their geographical orientation which is critical. Second in import- 
ance as a distinguishing factor is the topography, which leads to a sub- 
division of the two main slopes into ravines, slopes, and ridges. The 
fact that the differences between the ridges of the Windward and 
Leeward slopes are negligible has led to their combined treatment. 
The extreme summits of Blue Mountain and Sir John Peaks are treated 
separately, and the epiphytes have also been given special treatment, 
because their occurrence and distribution are more dependent upon 
vertical differences of conditions within the rain-forest than on the 
horizontal differences between the habitats recognized. 

The Windward Ravines exhibit to the most striking degree the char- 
acteristics of the rain-forest, and the other types have been treated 



28 A MONTANE RAIN-FOREST. 

fnmi the point ni view of their departure from them. So far as con- 
cerns their relative area, the Slope Forests far exceed the other types, 
bul their characteristics and vegetation are intermediate between those 
of the ravines and the ridges, and they do not possess the interest of 

either of the latter habitats. 

WINDWARD RAVINES. 

The ravines and valley bottoms of the Windward Slopes exhibit to 
the highest degree all those features of vegetation and climate which 
find expression in the term ''rain-forest," although they exhibit quite 
as strongly as do the other habitats the montane features which dis- 
tinguish the entire region from the lowland rain-forests. In the 
ravines, at least, are trees of stately size, forming a more or less con- 
tinuous canopy beneath which under-trees and shrubs form thickets 
varying in density according as the main forest canop}' is more or less 
open. The floor of the forest is covered with terrestrial ferns or 
flowering plants, which, in turn, vary in their stand with the density 
of the shrubbery and under-trees above them. Throughout the lower 
levels of the forest garlands of golden-brown mosses species of Phyl- 
logonium and Meteorium clothe the large trunks and hang from every 
twig in the undergrowth. On leaning trunks and horizontal limbs are 
crowded colonies of epiphytic ferns, orchids, and other flowering plants, 
from which hang pendant fronds of Hymenophyllwn or Elaphoglossum. 
In one spot the terrestrial herbaceous vegetation will far exceed the 
epiphytic ; in another masses of epiphytes may be found growing above 
a nearly bare forest floor, or again the epiphytes may be crowded out 
by the profuse growth of the climbing Marcgrama. Tree-ferns are 
abundant, standing singly or in groups, either beneath the shade of the 
largest trees or exposed to the sky. Their trunks form the support for 
climbing ferns and for masses of the most hygrophilous of the filmy 
ferns. 

A rather limited number of species of trees and shrubs, together with 
a relatively small number of herbaceous flowering plants, mingle with 
a large number of ferns, lycopods, mosses, and hepatics to constitute a 
type of forest which is far less rich in species and somewhat less rich 
in individuals than the best-developed lowland rain-forest. Varying 
greatly from spot to spot in the arrangement of its component species, 
the forest also exhibits a common tropical characteristic in the abund- 
ance in one spot of a species which may be rare for miles around. 

No picture of the Leeward Ravine forests is complete which does 
not portray the floating fog, in which it is enveloped so much of the 
time, and the reeking wetness which keeps its pads of mosses and hepa- 
tics always saturated and its foliage continously wet for days at a time. 
The height and constancy of the atmospheric moisture are the most 



SHREVE 



Plate 9 




VEGETATION OF THE RAIN-FOREST. 29 

potent factors in determining the character of the vegetation of the 
ravines, as well as in differentiating them from other habitats. Caused 
primarily by the abundant and well-distributed rainfall, as well as the 
prevalent fog, the humidity is maintained through the immense evapo- 
rating surface provided by the litter on the ground, the wet foliage, 
and the sponge-like masses of hepatics and mosses. Sheltered by the 
winds which sweep over the ridges and peaks, the Ravines are pro- 
tected also from the mid-day rise of temperature, both through the 
uppermost layers of foliage and through the fogginess, by virtue of 
which conditions the constancy of the high humidity is almost unbroken. 
Influences which tend to lower the humidity, and which operate through 
only a few hours, are offset by an increased rate of evaporation from 
the wet surfaces. Continued prevalence of such conditions through 
many days, however, serves to lower the humidity at the forest floor, 
with results fatal to many of the terrestrial herbaceous plants and the 
more hygrophilous epiphytes, as I had opportunity to observe in April 
1903, after three months with a rainfall of 3.45 inches (8.7 cm.), in 
which the normal fall is 16.32 inches (41.5 cm.). Coupled with the 
high humidity are temperature conditions of great constancy, the daily 
range varying from 5.8 to 7.6 F. 

The top of the Ravine forest, as seen from the adjacent slopes, 
presents an irregularity of surface much greater than that of the Slope 
and Ridge forest ; the largest trees standing well apart from each other, 
bearing crowded masses of epiphytes, and festooned with pendant 
mosses, while between them the canopy is formed by the crowns of 
smaller melastomaceous or rubiaceous under-trees or groups of tree- 
ferns. This irregularity of the canopy is due to the downfall through 
erosion of some of the largest trees and the slowness of the growth of 
the younger trees by which they will be replaced ultimately. The 
largest of the trees found only in Ravines are Solarium punctulatum, 
Guarea swartzii, Hedyosmum arborescens, and Turpinia occidental is, 
while together with them grow trees more frequent on the slopes, such 
as Hcemocharis hcematoxylon, Alchomea latifolia, Meriania purpurea, 
Ilex mojitana var. occidentalis, Lyonia jamaicensis, and Clethra occi- 
dentalis. The under-trees of the ravine forest are species which never 
reach the size of those just mentioned, and grow either in their shade 
or else themselves form the canopy of the forest. The commonest of 
them are Mecranium pur pur ascens, Bcehmeria caudata, Palicourea cmcea, 
Psychotria corymbosa, Eugenia biflora var. wallennii, Cestrum hirtum, 
and Miconia rubens. With these grow the tree-ferns, the commonest 
of which are Cyathea pubescens, Cyathea tussaccii, Cyathea furfuracea, 
and Cyathea insignis. A number of smaller under-trees and shrubs are 
equally characteristic of the lower layers of the ravine forest, notably 
Piper geniculatum, Piper fadyenii, TaurneforHa cymosa, Datura suaveo- 
lens, Acalypha virgata, Besleria lutea, and Senecio swartzii. 



30 A MONTANE RAIN-FOREST. 

The terrestrial herbaceous vegetation varies more with the physio- 
graphic age of the ravine than docs the arborescent vegetation, the 

initial ravines, with steep sides and rocky floor, differing from the 
Beqiiential ones with more open sides and a deeper soil. The beds of 
Steep and narrow ravine- are often covered with coarse stones to so 
great a depth a- to be almost devoid of large herbaceous plants, yet the 
Btones themselves are covered with Monoclea or with mats of Palla- 
ricinid, Riccardia, or Plagiochila, together with small filmy ferns, such 
as Trichomanes pyxidiferum, Trichomanes reptans, and Trichomam s 
hookeri. A few small flowering plants of pronouncedly hydrophilous 
character also occur in rocky ravines and on the steepest slopes that 
are deeply shaded, as Peperomia hispidula, Peperomia Jiliformis, Hydro- 
cotyle pusilla, Pilea brittonice, and Gesnera mimuloides. 

The beds of somewhat wider ravines provide soil of sufficient depth 
to support a dense growth of coarse ferns (see plate 2). The commonest 
and most wide spread species of ferns in such situations are Diplazitun 
celtidifolium, Diplazium costale, Asplenium alatum, Dennstoedtia sp., 
Diplazium altissimum, Diplazium brunneoriride, Dancea ja?naicensis, 
Asplenium rhizophorum, and Marattia alata, and with them grow less 
frequently or more sporadically a large number of other species. The 
wider and more shallow ravines have a less number of ferns in their 
herbaceous vegetation and a greater number of flowering plants, not- 
ably Pilea nigrescens, Peperomia turfosa, Peperomia obtusifolia, and 
Pilea parietaria, together with the less frequent Physurus hirtellus, 
Calanthe mexicana, Prescottia stachyodes, and Liparis elata. 

The trunks and limbs of the massive trees of the Windward Ravines 
bear a profuse epiphytic vegetation, which will be treated under a later 
heading. A small number of species of lianes are present, which are 
far from playing the role of the plants of this habit in the lowland 
forests. Marcgravia broivnei is by far the largest and most striking of 
the climbers, growing into the canopy of the forest, filling the crowns 
of the largest trees, and hanging in graceful festoons from their lower 
limbs. Its juvenile shoots are commonly seen growing closely appressed 
to smooth naked trunks, their small deltoid leaves forming a striking 
contrast to the long pinnate leaves of the adult shoots. Anthurium 
scandens is the only climbing aroid; its small simple leaves give it a 
far less important place in the physiognomy of the vegetation than is 
held by the species of Anthurium and Philodendron of the lowlands. 
Other frequent lianes are Smilax celastroides, Blakea trinervis, Metas- 
telma fawcettii, Metastelma atrorubens, Bidens shrevei, and Begonia scan- 
dens. Among the ferns Blechnum attenuatum and Polypodium loriceum 
are common in ravines and slopes alike, but seldom climb far above 
mid-height in the forest. The climbing filmy-ferns, Trichomanes radi- 
cans and Trichomanes scandens, are confined to deep shade in the 
narrowest ravines and seldom reach over 6 feet from the ground. 



SHREVE 



Plate 10 











a - 



/ "^ * 



VEGETATION OF THE RAIX-FOREST. 31 

WINDWARD SLOPES. 

On emerging from a ravine and climbing onto its slopes a number of 
notable changes in the vegetation are encountered at once; the stature 
of the forest is much less, varying from 30 to 50 feet (9 to 15 meters), 
and its canopy is much more open. The trees exhibit a striking diver- 
sity in trunk diameter, and all but the youngest have a down-hill 
inclination which brings many of the oldest into a nearly horizontal 
position. The leaning trees and downfallen trunks bring the epiphytic 
vegetation into the lower layers of the forest, and not infrequently 
colonies of bromeliads and epiphytic orchids may be found on the 
ground, rooted on the rotting remains of the trunk with which they 
fell. A more dense undergrowth and a more sparse herbaceous terres- 
trial vegetation characterize the slopes in comparison with the ravines, 
and the number of Pteridophytes is also much less, the climbing and 
epiphytic species being more observable, by reason of here occupying 
a place nearer the floor of the forest. The hanging mosses are absent, 
and the tree-ferns less frequent, at the same time that the thicket- 
forming ferns begin to be encountered. 

The Windward Slopes vary in their character, according as they are 
nearer the bottom of a valley or nearer a ridge, and indeed the vegeta- 
tion of the slopes is little more than a mean between the pronouncedly 
hygrophilous ravines and the open sub-alpine ridges. The slopes which 
lie just below gaps are similar to ravines, as may be noted to the north 
of Portland Gap and New Haven Gap, depressions in the main ridge 
through which clouds are rolling almost continuously. 

The forest of the Windward Slopes is made up predominantly of 
Clethra occidentalis, Podocarpus urbanii, V actinium mcridionale, Cyrilla 
racemiflora, Ilex montana var. occidentalis, Alchornea latifolia, and Bru- 
nellia comocladifolia. These vary from place to place in their relative 
abundance, but their order as above given is approximately that of 
their frequency of occurrence. With them and much less frequent are 
Hedyosmum arborescens, Clusia havetioides, Nectandra patens, Hoemo- 
charis hcematoxylon, Rhamnus sphcerospermus, Eugenia marchiana, 
Rapanca ferruginea, Weinmannia pinnata, and Cleyera theoidcs. A few 
under-trees and shrubs that are particularly common are Mecranium 
purpurascens, Tamonea rubens, Tournefortia ctjmosa, Palicourea crocae, 
Acalypha virgata, Haimocharis mllosa, Lisianthus latifolius, and the tree- 
ferns Cyathea furfuracea, Cyathea insignis, and the large-leaved but 
acaulescent Alsophila quadripinnata. 

The distinctly terrestrial herbaceous plants of the slopes are few as 
compared with the downfallen epiphytes, comprising conspicuously 
Pteris longifolia, Blcchnum capense, Polystichum dent icula turn, the broad- 
leaved grass Olyria latifolia, the sedges Rynchospora cggersiana and 
Uncinia hamata, together with Pilea parietaria, Lobelia assurgens, Pepe- 
romia baseUcpfolia, and Lycopodium reflexum. Among the downfallen 



32 \ \in\ i wi; i; \i N-FORE81 , 

epiphytes, by far t h* most common are species of Elaphoglossum 
Elaphoglos8um laHfolium, Elaphoglossum inojgualifolium, and Elapho- 
glossum peHolatum together with the orchid Stelis ophioglossoides, 
species of Dichoea, and the common bromeliad Caraguata sintenesii. 
Throughout the forest Chusquea abietifolia forms thickets or climbs 
over the lower trees, often making passage through the foresl difficult ; 
the only other common lianes arc Manettia lygistum, Cionosicys pomi- 
formiSf and Smilax celastroides. 

LEEWARD RAVINES 

The ravines of the leeward slopes of the Blue Mountains differ 
strikingly from those of the windward side, exhibiting few of the most 
pronounced characteristics of rain-forest. The general structure of 
the two types is similar, both in the stature of their trees and in the 
irregular canopy which gives place to abundant under-trees and shrubs. 
Many of the same species of trees occur in the ravines of the two sides 
of the range, and many of the epiphytes, but few of the terrestrial 
herbaceous plants. The most striking difference between the two 
ravine types is in the absence from those of the leeward side of garlands 
of hanging moss and the beds of epiphytic mosses and hepatics, the 
much scanter growth of epiphytes in general, together with the scarcity 
of tree-ferns, the inconspicuousness of filmy ferns, and the predomi- 
nance of herbaceous vegetation made up of a small number of fern 
species of a less hygrophilous character and a number of flowering 
plants. The leeward side of the range receives a lighter rainfall, has 
much less fog, and a reciprocally increased number of hours of sunshine, 
factors which combine to lower the atmospheric humidity and increase 
the insolation to a degree that modifies fundamentally the life condi- 
tions and makes the habitat an unfavorable one for very many of the 
species so common in the Windward Ravines, at the same time that they 
bring into the vegetation a number of trees, shrubs, epiphytes, and 
other plants, the range of w r hich extends down to 3,000 and 2,000 feet 
(915 meters and 610 meters), but does not cross the main ridge onto the 
Windward Slopes. By far the largest number of these middle-altitude 
forms are absent from the Leeward Ravines and find their optimal 
conditions in the still drier Leeward Slopes, on which the climate is 
nearer that of the lower altitudes. 

The commonest trees of this habitat are Gilibertia arborea, Alchornea 
latifolia, Ilex montana var. occidentalism Brunellia comocladifolia, Psy- 
chotaria brownei, and Psychotaria corymbosa. The commonest under- 
trees are Bcehmeria caudata, Datura suaveolens, Phenax hirtus, Acnistus 
arborescens, Piper geniculatum, and Malvaviscus arboreus. The herba- 
ceous vegetation is dominated by Pilea grandifolia and an assemblage 
of species of Asplenium and Dryopteris notably Asplenium pteropus, 
Asplenium lunulatum var. striatum, Asplenium obtusifolium, Asplenium 



SHREVE 



Plate 





SHREVE 



Plate 12 




/ ~ 



'/. - 



SHREVE 



Plate 13 







-3 ." 






SHRl'Al-. 



Plate- 14 









w 


r 



_ 






r -- 



A. Looking over Leeward Slopes and ruinate in the vicinity of Cinchona. The isolated dark trees 

are Juniperus barbadensis. 




B. Bridle path through Leeward Slope Forest, with overhanging massed ol the climbing band 

qui a abu tifolia. 



VEGETATION OF THE RAIN-FOREST. 33 

cristatum, and Dryopteris effusa, Dryopteris patens, Dryopteris ampla, 
and other species for which it has not been possible to secure determi- 
nations. Peperomia turfosa, Pilea parietaria, Rynchospora eggersiana, 
Calanthe mexicana, Spiranthes sp., and several other orchids are infre- 
quent in occurrence. 

LEEWARD SLOPES. 

Both the climatic conditions and the vegetation of the Leeward 
Slopes differ considerably between the lowest altitudes which arc being 

considered and the upper slopes in the vicinity of the main ridge of 
the Blue Mountains. The latter resemble in many respects the ridges, 
to be described presently, and differ from the former not so much by 
reason of their difference in altitude as on account of the greater rainfall 
at the higher slopes and the fact that they are enveloped in fog during 
a good share of the time that the lower slopes are in sunlight. What i- 
to be said of the Leeward Slopes accordingly relates to the lower alti- 
tudes, while the higher ones that is to say those within 500 vertical 
feet (153 meters) of the main ridge are comprised in the ridge type 
of forest. 

The Leeward Slopes depart still more than the Leeward Ravines 
from the typical rain-forest which has been described. An arborescent 
flora richer than that of the Windward Ravines and Slopes form- a 
forest of low stature, in which individuals of large and small trunk 
diameter are intermingled to form a closed canopy. There is little 
distinction between the crowns of the largest trees and the foliage of 
the smaller trees and shrubs, so that there is frequently a solid mas> 
of foliage from the canopy to the ground. The hygrophilous mosses 
and hepatics are scarce, and the epiphytic vegetation is scant and con- 
fined to the more xerophilous forms of the ridge forest. Lianes are 
abundant, as are also a number of loranthaceous parasites. The ter- 
restrial herbaceous species are largely phanerogamic, while the pt en- 
dophytic ones include a large number of species of fern- represented by 
infrequent individuals, and a small number of lycopodiums which are 
extremely abundant . 

The trees of the Leeward Slopes are in part species which also occur 
on the slopes of the windward side, together with others which range 
upward from far below our area. The most common arc: ('It thru 
orrulcnlnlis, Yairinium meridionale, Ilex montana var. occidentaUs, 
Alchorw-a hilifolia, Brunellia comocladifolia, Rapaneaferruginea, Cyrilla 
racemiflora, Juniperus barbadensis, Cleyera theoides, Lyoniajamaicensis, 
( 'itharexylum caudatum, Viburnum viUosum, Viburnum alpinum, Eugt nia 
harrisii, Dipholis montana, Daphnopsis tinifolia, Gilibertia arborea, 
Oestrum sp., Heterotrichum patens, Psidium montanum, and Tamonea 
rubens. A large number of -mailer trees and shrubs are characteristic 
of these slopes, some of them dominating the areas of ruinate which are 



34 A MONTANE RAIN-FOREST. 

returning to forest. Commonest of these are: Bachharis scoparia and 
Dodonooa angustifolia; others are Garrya fadyenii, Acalypha virgata, 
Oreopanax capitation, Bocconia frutescens, Myrica microcarpa, Malva- 
viscus arboreus, Eupatorium parviflorum, Micromeria obovata, Hedyos- 
mum nutans, and Vernonia intonsa. 

The herbaceous vegetation, although rich in species, is not so rich 
in individuals as the most luxuriant spots in the Windward Slopes, and 
is characterized by the entire absence of all the most hygrophilous 
species of the northern side of the range. Thickets of Gleichenia pecti- 
nata and Odontosorea aculeata are frequently encountered, particularly 
at the higher altitudes, and beneath them the ground is bare of vege- 
tation and very densely shaded. Pteridium aquilinum also frequently 
forms thickets, but they are much more open and accompanied by 
sedges and grasses. 

In the more heavily wooded portions of the Leeward Slopes the 
commonest herbaceous plants are Pilea grandifolia, Uncinia hamata, 
Rynchospora eggersiana, and Rynchospora polyphylla. On steep banks 
and shaded rocks may be found Pilea microphylla, Pilea parietaria, 
Peperomia turfosa, Peperomia rupigaudens, Vittaria lineata, and Antro- 
phyum lineatum. In more open situations Lycopodium clavatum, 
Lycopodium cernuum, and Lycopodium fawcettii form such extensive 
growths as to be very conspicuous. Begonia nitida and Begonia acumi- 
nata are frequent on steep slopes, and the orchids Epidendrum cochle- 
atum, Epidendrum ramosum, and Epidendrum verrucosum. The com- 
monest ferns are Polystichum struthionis, Dryopteris effusa, Blechnum 
capense, Nephrolepis cordifolia, Blechnum occidentale, and Pteris longi- 
folia, to which might be added over one hundred that occur sporadically. 
Other plants of interest which give character to this habitat are Rubus 
alpinus, Iresine celosioides, Lobelia caudata, Ascyrum hypericoides, 
Liabum umbellatum, Spiranthes elata, Polypodium crassifolium, and 
Lantana camara. 

The number of species of lianes is greater in these forests and the 
ruinate than it is on the Windward Slopes, but they are no more con- 
spicuous as an element of the vegetation. They comprise commonly: 
Smilax celastroides, Passiflora sexfiora, Passiflora pendulifiora, Metas- 
telma atrorubens, Metastelma ephedroides, Ipomoea triloba, Manettia 
lygistum, and the herbaceous woolly-leaved Relbunium hypocarpium. 
The loranthaceous parasites are also conspicuous, including Loranthus 
parvifolius, Phoradendron flavens, Dendrophthora cupressoides, and Den- 
trophthora gracilis. 

The outcroppings of limestone scattered over the Leeward Slopes 
usually project above the shade of the forest and are occasionally 
large enough to support small trees of Juniperus barbadensis, bushes of 
Baccharis scoparia and Micromeria obovata. In their crevices and 
pockets occur a number of plants, some of which are not found else- 



SHREVE 



Plate 15 




VEGETATION OF THE RAIN-FOREST. 35 

where in the region, others of which are epiphytes at lower altitudes, 
as: Peperomia verticillata, Tillandsia complanata, Isochilus linearis, Bryo- 
phyllum calycinum, Epidendrum verrucosum, Polypodium incanum, 
Polypodium lanceolatum, Polypodium plumula, Cheilanthes microphylla, 
and Asplenium dimidiatum. 

THE RIDGES. 

The Ridge Forest of the Blue Mountains is stunted, open, and 
relatively xerophilous in the entire make-up of its vegetation. It pos- 
sesses few of the species characteristic of ravines, at the same time that a 
distinct set of characteristics are the salient ones in determining its 
physiognomy. The main ridge of the Blue Mountains at 5,600 to 
6,000 feet altitude exhibits the most marked type of Ridge Forest, 
excepting at the low gaps. Radiating from the main ridge along the 
principal lateral ridges and from them in turn along the lesser water- 
partings extend the narrow stretches of Ridge Forest, retaining much 
the same character down to 4,500 feet and differing only in minor 
particulars on the windward and leeward sides of the range. On 
leaving any part of the Ridge Forest and descending to a distance of 
100 feet the characteristics of the slopes will be found to prevail. 

The Ridge Forest presents a very level canopy when viewed at a 
distance, but it varies greatly in the density or openness of its stand of 
trees. In the most dense stands, however, the trees are sufficiently 
far apart for their crowns not to meet, which fact, together with the 
sparsity and openness of the shrubby vegetation, allows considerable 
light to reach the forest floor. The trees vary from 18 to 30 feet in 
height, but are of incommensurate trunk diameter, often making 2 and 
3 feet in thickness with a height of 16 to 20 feet. The largest trunks are 
bent and gnarled or prostrate on the ground, and so interlocked with 
dead and decaying trunks that the forest floor is seldom clear for a 
space as much as 15 feet square (see plate 17). 

The under-trees are scant, but young individuals of the principal 
tree species are common, as are also xerophilous shrubs, chiefly occur- 
ring in the most open parts of the forest. The more open the forest 
the more completely is it occupied by the bamboo, which literally fills 
the forest from the ground to a height of 6 or 8 feet; or in other open 
places the bamboo is absent and dense thickets of ferns cover the 
ground to a depth of 4 or 5 feet, excluding all smaller vegetation. 
Only in the portions of the Ridge Forest with a closed canopy is the 
floor clear enough to give space to a small number of herbaceous species, 
which are chiefly ferns and the sedges Rynchospora polyphylla and 
Rynchospora elongata. 

The epiphytic vegetation is not conspicuous, indeed hardly as much 
so as are the parasitic Loranthaceae, although actually embracing a 
considerable number of species. These are mostly bromeliads and 
small species of Polypodium and Liparis, while mosses, the hepatic 



36 A MONTANE RAIN-FOREST. 

Herberia, lichens, and blue-green algs form a considerable portion of 
t 1h i epiphytic growth <>n the slender limbs of the largest trees. On 
the prostrate trunks and lower limbs are thick mats of mosses and 
hepatics, or colonies of Hymenophyllaceffi, in which often grow larger 
ferns, orchids, and lycopods. 

The few moist depressions alluded to as occurring on the main ridge 
are tilled with Sphagnum lesucurii and Rynchospora polyphylla, hut an- 
not without trees growing in their midst and have no species which are 
peculiar to them. Sphagnum is common elsewhere in the Blue Moun- 
tains, both on the ground and growing as an epiphyte, while on the 
summit of Guava Ridge, in the Port Royal Mountains, is an open bog, 
filled with sphagnum and having a close resemblance to North Tem- 
perate peat bogs. 

The commonest trees of the Ridge Forest, together forming perhaps 
one-fourth of the stand, are Podocarpus urbanii and Clethra alexandri: 
very abundant are: V actinium meridionale, Rapanea ferruginea, Wein- 
mannia pinnata, Cyrilla racemiflora, Myrica microcarpa, Ilex montana 
var. occidentalis, and Eugenia alpina. I^ess frequent are: Cleyera the- 
oides, Eugenia lateriflora, Clusia haretioides, and Rhamnus sphaeros- 
permus. The degree to which many of the above species are present 
only as stunted individuals of 4 to 8 feet in height is indicated in plate 
19 and plate 20. Ilex obcordata is a common shrub sometimes attaining 
to the height of a tree and, with Eugenia alpina, exhibiting the smallest 
leaves of any trees in the region (see plate 20 A). A form of Palicourea 
crocea is common, together with Miconiarigida, Wallenia crassifolia, and 
Lisianthus latifolius. The Composite contribute several shrubs to the 
ridge vegetation, notably Vernonia divaricata, which forms extensive 
thickets in open stands of forest, particularly on the main ridge between 
Sir John and Mossman's Peaks, Eupatorium dalea, Vernonia arbor- 
escens, Senecio fadyenii, and Eupatorium crilonijorme . One of the most 
striking plants of the ridges is Lobelia martagon, which has a woody 
stem branched once, growing to a height of 7 feet and bearing tufts of 
leaves at the ends of its branches, with its spikes of dark-red flowers. 
The exposure of the ridges to high wind is probably accountable for 
the absence of tree-ferns, as just below the most exposed of the ridges. 
in forest of similar character, may be found Cyathea furfuracea and 
Cyath ea in sign is . 

The thickets of ferns are made up chiefly of Gleichenia jamaicensis, 
Gleichenia bancrojtii, and Odontosorea aculeata, but are frequently also 
formed by Pteridium aquilinum, Histiopteris incisa, Pteris deflexa, and 
Hypolepis nigrescens. Within the denser forest the open floor is most 
conspicuously covered with Rynchospora polyphylla and Blechnum 
capense, in addition to which Peperomia basellcefolia, Pteris longifolin. 
and Plagiogyria biserrala occur, together with downfallen epiphytes and 
the seedlings and suckers of the trees. 



SHREVE 



Plate 16 




i~ 2: 



?.'- 



- ; 






VEGETATION OF THE RAIN-FOREST. 37 

THE PEAKS. 

An examination of Blue Mountain Peak and Sir .John Peak showed 
them to be essentially identical in their vegetation in spite of their 
difference of 1 ,200 feet in altitude. In flora the peaks perhaps differ 
somewhat more from the lower parts of the range than they do in their 
vegetation. Several species have been described which are supposed 
to be confined to the summit of Blue Mountain Peak or to its higher 
slopes, but so little is known of the regions immediately surrounding 
the peak and off the single bridle road by which the summit is acces- 
sible that these species may be turned up elsewhere. Indeed, the peak 
possesses no more endemic forms than do many other areas of the 
same size in the island. That many of the mountain species are 
absent from Blue Mountain Peak is altogether likely, although no one 
has ever made a sufficiently thorough examination of the locality to 
be warranted in stating what these species are. 

The vegetation of the Peaks exhibits a mere accentuation of the 
characteristics that have been described for the Ridges the forest is 
low and extremely open, the tallest trees seldom exceeding 20 feet, 
with under-sized individuals of the dominant trees and various shrubs 
forming the bulk of the stand, thickets of Gleichenia and Pteridium 
occupying the open places. The essential similarity of the vegetation 
to that of the Ridges is due to the high winds to which the two habitats 
are alike subjected and to the possible fall of soil-moisture content 
previously alluded to. 

The characteristic trees of the summit of Blue Mountain Peak are 
Clethra alexandri, Podocarpus urbanii, Gilibertia nutans, Y actinium 
meridionale, Ilex montana var. occidentalism and Eugenia alpina. Less 
frequent, and usually occurring as shrubs, are: Ilex obcordata, Cleyera 
theoides, Weinman nia pinnata, Viburnum tillosum, and Rhamnus sphac- 
rospermus. A striking under-tree, apparently confined in occurrence 
to the summit of Blue Mountain Peak, is Senecio laciniatus, which has 
a soft, woody stem, large leaves, and very conspicuous yellow flowers. 
In addition to it all of the composite shrubs mentioned as occurring 
on the Ridges are important components of the scrub which covers the 
highest peaks. In addition to the thicket-forming ferns, Gleichenia 
jomaicensis and Odontosorea aculeata, common throughout the highest 
parts of the Ridge forest, Pwsia viscosa, Hypolepis pulcherrima, and 
Hypolepis repens are common at the highest altitudes. Almost equally 
conspicuous with the fern thickets are the beds of Lycopodium, M>me- 
times 20 to 40 feet in diameter, and made up of Lycopodium clavatum, 
Lycopodium fawcettii, and Lycopodium cernuum. In the absence of 
fern or lycopod thickets, Blechnum capense and Rynckospora pallida 
are the characteristic inhabitants of the forest floor, while in more 
deeply shaded situations Asplenium lunulatum and Pilca parietaria 
var. alpestris are common. With the exception of the bromeliads 



38 A .MONTANE RAIN-FOREST. 

TiUandsia incurva and Caraguata sintenesii, the epiphytic plants at the 
high peaks are exclusively small orchids and ferns, polster-forming 
mosses, xerophilous hepatics, lichens, and Cyanophyceoe. 

The summit of John Crow Peak reaches nearly the altitude of Sir 
John Peak, but is strikingly different from it in its vegetation, owing 
to its summit being part of a limestone dyke running southeast into 
the valley of the Clyde River. The bare rock of the summit is eroded 
into a honeycombed surface with knife-like edges and pockets of soil, 
in which is supported a stunted and open forest. Cyrilla racemiflora, 
Rhamnus spharrospermus, and Eugenia fragrans are here quite common, 
to the exclusion of the familiar species of the other peaks. Fagara 
hartii, Brunfelsia harrisii, Eugenia marchiana, Acalypha virgata, Gym- 
nanthes elliptica, Chcenocephalus sp., and Eupatorium critoniforme are 
all either peculiar to this peak or characteristic in its vegetation. 
Drought-resistant shrubs with prodigious thickets of Chusquea domi- 
nate the upper slopes of John Crow Peak to the almost total exclusion 
of all the forms characterizing the rain-forest by which it is surrounded. 

EPIPHYTES. 

The epiphytic plants occupy quite as conspicuous a place in the 
total assemblage of vegetation in the Montane Rain-forests as they do 
in any of the lowland plant formations of Jamaica. At the lower 
altitudes to windward of the Blue Mountains the lofty forest is rela- 
tively poor in epiphytes excepting in the tops of the trees, where Brome- 
liacese and Orchidacese are the commonest forms. In the savannas of 
the southern coast and in the central part of the island the species of 
TiUandsia are by far the most prominent epiphytes, with which are 
usually found a number of Orchidacese and the single species of Bro- 
melia present in the island. In the rain-forest of the mountains every 
type of epiphytic plant is represented, the bromeliads, the orchids, a 
number of woody forms, ferns of every description from the most 
delicate Hymenophyllaceae to extremely small drought-resistant poly- 
podiums, flowering plants, both hygrophilous and succulent, as well as 
mosses, hepatics, and lichens. 

Schimper 1 pointed out the differences between the epiphytic vege- 
tation of the forest floor and the canopy, and I have shown in a previous 
paper that a similar difference exists in the case of the Hymenophyl- 
laceae and that it is determined by the vertical difference between the 
climate of the floor of the forest and its canopy, a factor which is 
operative in the case of all the epiphytic vegetation. The contrast 
between the epiphytes of the lowest level of the forest and the tree- 
tops is greater than in the lowland forests, due, of course, to the 

Schimper, A. F. W. Die Epiphytische Vegetation Amerikas. Bot. Mitth. aus den Trop., 
Heft 1, 18S8. 

2 Shreve, F. Studies on Jamaican Hymenophyllaceae. Bot. Gaz. 51 : 1S4-209. Mar., 1911. 



SHREVE 



Plate 17 




SHREVE 



Plate 18 







5^ 






u 5 

- -= 



C . 

= - 
ri 5 

. - ~ 

- a 

. 

a. u 

* 



- y 

- L 

- 






SHREVE 



Plate 19 




SHREVE 



Plate 20 






w 




VEGETATION OF THE RAIN-FOREST. 39 

higher and more constant humidity at the floor in the mountain forests. 
The epiphytes of the lowest level are pronounced hygrophytes, confined 
to that level by its favoring conditions of humidity and frequent 
wetness. The mid-level forms are somewhat drought-resistant or else 
confined to the proximity of water-storing mats of bryophytes, or 
they may have a water-storing tissue. The epiphytes of the topmost 
level are pronouncedly xerophilous, with either water-storing or water- 
catching structures, or else they are small and coriaceous. 

The Windward Ravines exceed by far all of the other mountain 
habitats in the wealth of their epiphytes, because in them can be found 
not only their own peculiar forms, but in the tops of the tallest trees 
are to be found the forms characteristic of the Ridge Forests, while at 
mid-height in the Ravines are to be found those characteristic of the 
Slopes. 

The commonest terrestrial ferns, orchids, and species of Pilea are 
not very commonly found as epiphytes, even at the lowest level in the 
forest, but the succulent Peperomias Peperomia basselcefolia and Pepe- 
romia filiformis with the non-succulent Peperomia hispidula, are low 
epiphytes, growing with Trichomanes capillaceum, Trichomanes hookeri, 
Trichomanes pyxidiferum, and Hymenophyllum fucoides. Such filmy 
ferns as Hymenophyllum asplenioides, Hymenophyllum tunbrigense, 
Hymenophyllum crispum, and Hymenophyllum polyanthos grow fre- 
quently on rather bare trunks, as do also Polypodium suspensum and 
Polypodium cultratum, forms distinguishable by their pendant fronds. 
In the case of the majority of forms, however, which occur more than 
a few feet above the ground, the existence of a moss substratum is 
essential to their occurrence. The more resistant filmy-ferns, Hijmeno- 
phyllum polyanthos, Hymenophyllum crispum, and Hymenophyllum fuc- 
oides, are very common at middle elevations in the forest, growing in 
beds of liverworts, beneath which such pendant forms as Hymeno- 
phyllum sericeum, Hymenophyllum axillare, Elaphoglossum squamosum, 
and Elaphoglossum villosum are common in occurrence. 

The largest of the epiphytes is Sciadophyllum brownei, an araliaceous 
plant sometimes growing independently, sometimes a half-climber, but 
more frequently epiphytic at mid-level in company with the gesner- 
aceous Columnea hirsuta and the melastomaceous Blakea trinervis 
also often rooted in the soil. Seedlings of Clusia haretioides are also 
frequent as epiphytes, seedlings of other trees being rare off the ground. 
Peperomia obtusifolia var. is conspicuously frequent, as are also some 
of the numerous species of Elaphoglossum (Elaphoglossum latifolium, 
Elaphoglossum incequalifolium, and Elaplioglossum pallidum) and the 
striking Lycopodium taxifolium. The larger epiphytic orchids are very 
numerous, although there are but few species of them. Stelis ophio- 
glossoides and Dichcea granwtea are forms with water-storing Leaves 
and thin roots, while Dichcea glauca has thin leaves and stout roots with 



10 A MONTANE RAIN-FOREST. 

well-developed velamen. Epidendrum verrucosum has water-storing 
leaves and false bulbs, and biparis (lata has water-storing false bulbs 
and thin leaves, and seldom emerges far from the forest floor. 

In the highest level of the tree-tops the epiphytes are small plants 
in every case excepting the common tank-epiphyte, Caraguata rinte- 
tenesii, which also grows in the mid-levels. The small orchids of the 
tree-tops are all provided with water-storing tissue in their leaves, 
commonest among them being Lepanthes concinna, Lepanthes triden- 
tata, Lepanthes concolor, and PlewothaUis sp. The small ferns growing 
with these orchids are mostly species of Polypodium Polypodium 
gramineum, Polypodium marginellum, and Polypodium serrulatum being 
common. A large white Usnea and a smaller yellow species, together 
with the hasidiomycetous lichen Cora pavonia, are common in the tree- 
tops, particularly on the Ridges at higher elevations, where they grow 
with the polster mosses Macromitrium and Sclotheimia. 

To proceed from a Windward Ravine up through Slope forest to a 
Ridge would bring to view in the lower levels of the forest the same 
transition in epiphytic vegetation that might be seen by climbing a 
tall tree in a ravine, except that lichens are not conspicuous in tin- 
canopy of the Ravines, and the mid-height epiphytes are often found 
in favorable spots on the ridges. The importance of a living water- 
conserving substratum for the occurrence of the mid-height epiphytes 
is everywhere apparent on the slopes and ridges. 

I have shown in an earlier paper 1 something of the comparative 
power of drought resistance in Stelis ophioglossoides, a typical loaf- 
storage epiphyte, and Caraguata sintenesii a typical tank-epiphyte 
(incorrectly designated as Guzmania tricolor in the paper alluded to). 
"When deprived of its catch of water Caraguata exceeded Stelis in its 
ability to persist in the absence of renewed supplies of water while kept 
in the laboratory for fifty days. During the longest periods of drought 
to which these forms are apt to be subjected Caraguata would be 
exposed to conditions more favorable to water-loss than would Stelis 
in its mid-height position in the forest, so it is probable that under 
natural conditions the two types would both meet the limit of their 
resistance at the end of six or seven weeks without renewed supplies 
of water, an extreme condition which the weather records would indi- 
cate has happened but once in the past thirty-nine years, this occasion 
being in the vicinity of New Haven Gap in the spring of 1892 (see p. 15). 

With such capacity for drought resistance may be contrasted the 
character of the most hygrophilous of the filmy-ferns, such as Tricho- 
manes capillaceum and Trichomanes rigidum, to which the total depriva- 
tion of water for seventy-two hours is fatal, provided the surfaces of 
the leaves are dried off at the outset of the period and the humidity 

'Shreve, F. Transpiration and Water Storage in Stelis ophioglossoides. Plant World, n: 
165-172, Aug. 190S. 



SHREVE 



Plate 21 




RELATION OF CONDITIONS TO HABITAT DISTINCTIONS. 41 

is playing through its usual range in the vicinity of Cinchona (see plate 
22). That other species of the Hymenophyllaceae have acquired scmi- 
xerophilous characteristics which enable them to persist in the mid- 
levels of the forest in company with Caraguata (see plate 22) and to 
endure the same conditions to which it is liable, is one of the most 
striking features of the rain-forest. 

THE RELATION OF PHYSICAL CONDITIONS TO HABITAT 
DISTINCTIONS IN THE RAIN-FOREST. 

During my visit to the Blue Mountains in the winter of 1905-0(3 I 
carried on instrumentation designed to give some evidence as to the 
degree and manner in which the climatic conditions within the rain- 
forest depart from the normal conditions of the open slopes at Cinchona 
on which the longer series of data was secured which have already been 
presented; and also to determine what some of the differences of con- 
ditions are that may be responsible for the distinctions in the vegeta- 
tion of the habitats that have been described. 

It requires but a casual visit to the region to realize that the most 
salient characteristics of the vegetation are determined by the high 
rainfall unbroken by a pronounced dry season together with the 1 
high percentage of cloudiness and fog, with all the subsidiary condi- 
ditions of moist soil, moist atmosphere, small percentage of insolation, 
wetness of foliage and the like, which follow in their train. Further- 
more the moisture conditions are the most important set of differential 
factors in determining the diverseness of the several habitats. 

Rainfall readings are almost meaningless for a region in which, as 
here, ten showers of two hours' duration each may give only a total 
fall of 1 to 2 inches, whereas on another day a single fall of two hours' 
duration may give the same amount, with a totally incommensurate 
effect on the other moisture conditions and on the vegetation. Further- 
more, a light rain followed by several days of continuous fog will have 
a very different significance from a heavier fall followed by two or three 
hours of insolation. The irregularity of the rainfall (see p. 15) together 
with the fact that the moistness of the atmosphere, the wetness of the 
foliage, and to an extent even the moistness of the soil, are due as much 
to fog as to actual precipitation of drops large enough to be called rain, 
gives the rainfall figures only the most general bearing on t he conditions 
present. So well distributed is the rainfall, so low the evaporating 
power of the air, and so unbroken the vegetational covering, that the 
state of moistness of the soil is a factor which can be safely neglected 
throughout periods of normal weather. I have already called atten- 
tion to the occasional periods of very light rainfall, during which it is 
possible for the soil moisture of the ridges and peaks to fall to an extent 
that would make this factor one of importance. I had an opportunity 



42 A MONTANE RAIN-FOREST. 

in 1903 to observe the effects of a prolonged season of dryness, but the 
chance to secure soil-moisture determinations for such a period has not 
recurred since I have been interested in the subject. 

My instrumentation has, accordingly, centered in th<' determination 

of the atmospheric moisture conditions, extending also to the securing 
of air and soil-temperature readings. Automatic traces of the daily 
play of the humidity conditions were secured by use of a hygrograph, 
which was combined with a thermograph in the type of double register 
made by Friez. Owing to the practical exigencies of the work, only 
one of the instruments was used, which was moved from place to place 
to secure the several records, thereby making it impossible for me to 
obtain simultaneous readings from different stations. The general 
uniformity of the weather conditions through the winter of 1905-06 
kept this circumstance from seriously impairing the comparableness 
of the various record slips. The instrument was installed about 3 feet 
from the ground, on a portable framework of boards, and protected 
by a white water-proofed canvas placed so as to be at least 1 foot from 
the instrument above and at the sides, while the ends, together with the 
open base, gave a free access of air. A soil thermograph of the Hallock 
t}-pe, made by Friez, was also used, being usually installed with the 
double register or else in a similar manner. The cylinder was buried 
at a depth of 1 foot in all cases; a hole was dug, from which a tunnel was 
made to one side for the cylinder, and the earth was packed in naturally. 
In this manner the soil above the cylinder was left undisturbed. 

The hydrograph was corrected at the beginning and end of each week 
in accordance with sling-psychrometer readings. The thermograph 
was also verified in its reading twice for each sheet; the soil thermo- 
graph three times for the period of five months over which it was used. 
The thermograph and hygrograph traces presented in the accompany- 
ing plates have been redrawn from the originals. This has lost them 
something of their detail, but has been necessar}' to the incorporating 
of the corrections, as well as to the manner of their reproduction. 

During the summer of 1909 a number of readings were taken at 
Cinchona and in the rain-forest with the type of atmometer devised by 
Livingston. 1 The atmometers were protected from rain by suspending 
a small pane of glass horizontally at a few inches above the tip of the 
cup. The error due to the wetting and impact of rainfall in the ordi- 
nary atmometer when not covered by glass is considerable, and is most 
satisfactorily obviated by the use of the rain-correcting type of instru- 
ment more recently invented by Livingston. 2 Readings with an instru- 

Ujivingston, B. E. The Relation of Desert Plants to Soil Moisture and to Evaporation. Carnegie 
Inst. Wash. Pub. 50, 1906. Also: Operation of the Porous Cup Atmometer. Plant World, 
13 : 111-119, 1910. 

2 Livingston, B.E. A Rain-correcting Atmometer for Ecological Instrumentation. Plant World, 
13 : 79-82, 1910. 



SHREVE 



Plate 22 




A. Shoot.> of Il(.r obcordata (left) and Eugenia alpina, the smallest-leaved tree- of the highest i>r:ik- 




B. Series of potted plant- as used in transpiration experiments. From lefl to right: Pilea n 

Peperomia turfosa, Peperomia baseUaefolia, Diplazium celtidifolium, Asplenium alatum, and porous 

cup atmometer mounted for weighing. 



RELATION OF CONDITIONS TO HABITAT DISTINCTIONS. 43 

ment of this type were taken by Brown 1 at my Windward Ravine 
station in the summer of 1910, extending through four weeks. 

In the still air of the floor of the rain-forest, where the temperature 
ranges through less than 10 a day, the atmometer is in effect a 
hygrometer, registering the cumulative evaporation of the longer inter- 
vals when the humidity falls below the prevalent high percentages. 
The ratio of the rate of evaporation from a free water surface to that 
from a standard cup has been found to be 0.76 at Cinchona as compared 
with 1.15 at Tucson. This points to a difference in the character of 
the evaporating water film under the two diverse climates, the film 
probably being discontinuous in the drier climate, occupying only the 
pores of the cup, while it is continuous in the moist climate, occupying 
the entire surface. The difference between the dry look of the surface 
of cups in operation at Tucson and their moist look when in operation 
at Cinchona corroborates this explanation. The existence of a greater 
surface film would have the effect of increasing the evaporating surface 
of the cup, and would accordingly lower its ratio to a free water surface 
as compared with this ratio determined in an arid climate. While 
these considerations make it necessary to apply a considerable correc- 
tion to atmometer readings from widely diverse climates before com- 
paring them, they do not at all invalidate the comparableness of 
readings taken under similar humidity conditions. In rain-forest 
ravines the atmometer is subject to the condensation of moisture onto 
its evaporating surface, whenever evaporation cools this a few degrees 
below the air temperature. The condensation stops evaporation and 
cooling, and permits the surface of the cup to warm up again and 
presently to resume evaporation. The low rates of evaporation obtain- 
able with the atmometer in Windward Ravines are undoubtedly some- 
what lower than they should be for this reason. 

After repeated observations with the hygrograph and sling psy- 
chrometer, I am convinced that saturation, or even humidities as high 
as 97 to 99 per cent, are extremely transitory states of the atmosphere 
in the most moist situations in the rain-forest. Saturation must pre- 
cede precipitation; and the condensation of moisture on the foliage of 
plants often takes place in the deep forest. As soon as precipitation 
or condensation occurs, there is a fall in the humidity and it naturally 
rises again but slowly, for although the extent of wet surfaces capable 
of adding by evaporation to the moisture of the air is very great, the 
high humidity itself retards such evaporation. Cloudiness is an imj K>r- 
tant factor in influencing humidity as well as is fog. The passage of 
small clouds over the face of the sun causes immediate and pronounced 
rises in humidity, due in great measure to the sudden fall of temperature 
which may be too transitory to affect the sluggish ther mograph. 

iBrown, W. H. Evaporation and Plant Habitat* in Jamaica. Plant World, 13 : 21 10. 



I I a MONTANE RAIN-FOREST. 

HUMIDITY. 

I am doI able to give any figures or records bo show satisfactorily 
what differences there may be betweeD the moisture conditions a1 
different altitudes on the Windward Slopes of the Blue Mountain 

Flange. The rainfall of 130 inches at Bort Antonio is due to heavy 

showers which are of ten confined to the vicinity of the coast. Localities 

off the coast at 1 ,000 to 3,000 feet altitude receive less than that amount 
of rain. The upper /.one of heavy rainfall begins at about 4,000 feet, 
and extends to the summit of Blue Mountain Peak. The fact that the 
fall for New Haven Gap is 113 inches and that for Blue Mountain 
Beak 1(')S inches indicates that the fall increases steadily with increase 
of altitude. Even more important than the rainfall conditions is the 
behavior of the cloud mass which is so characteristic of the windward 
slope. Judging from my repeated visits to the windward side of the 
range, from one to three times a week at all seasons of the year, I may 
hazard the estimate that during February, .Inly, and August these 
slopes are enveloped in cloud for 30 per cent of the daylight hours, 
and during the other months of the year for 70 per cent of them. The 
nights are always clear, and it not infrequently happens in the winter 
months that lower humidities occur at night than those prevalent dur- 
ing the day. Several times I have watched the sunrise from Blue 
Mountain Peak or from the Main Ridge in the vicinity of Sir John 
Peak, and have noticed that it was only 5 to 15 minutes thereafter 
when clouds began to form. An hour to two hours after sunrise there 
would be a solid cloud blanket over the entire north slope. Detached 
fragments from this cloud mass are being continually blown across the 
main ridge and they melt quickly as they are borne down over the 
sunny leeward slopes. I feel assured that on the windward slopes 
above the lower limit of our area at 4,500 feet there are not any dif- 
ferences of moisture conditions of a kind or amount capable of influ- 
encing the vegetation. The cloud blanket gives a uniformity to the 
conditions, which can scarcely be rendered pronouncedly different by 
a rise of rainfall from as high an amount as 113 inches to 108 inches per 
annum. 

The percentages of fog during the day at Cinchona are roughly 
10 per cent for February, July, and August, and 30 per cent for the 
other months, and it is to this difference rather than to its slightly 
lower rainfall of 105 inches that we must look for the basis underlying 
the principal habitat distinction which I have made that between 
the leeward and windward sides of the range. The cloud blanket 
seldom settles for any length of time over localities on the leew r ard 
side below r 4,500 feet, and the rapidity with which the rainfall dimin- 
ishes below that altitude is shown in the 67 inches fall for Resource, 
which is located southof Cinchona, at 3,700 feet (1,128 meters) elevation. 



RELATION OF CONDITIONS TO HABITAT DISTINCTIONS. 45 

The fog is of two sorts a moving, wind-driven, relatively dry fog 
seldom accompanied by rain, and stationary fog of high humidity and 
often accompanied by drizzling rain or a heavy downpour. I have 
observed on several occasions that the moving fog may pass without 
influence on the humidity of the air. At Cinchona, on the late after- 
noon of February 28, 1906, I obtained identical psyehrometer readings 
before, during, and after the passage of a wind-blown mass of fog, 
the humidity being 94 per cent. 

The continual high humidity of the Windward Ravines is exhibited 
in plate 24, figure B, and plate 25, figure B, both of which were secured 
at the floor of ravines in the vicinity of Morce's Gap. Climatic and 
topographic conditions join with the sheltering effect of the forest 
itself and its immense evaporating surface to give to this habitat con- 
dition of moistness which can hardly be exceeded in any locality on 
the globe. The degree to which the surrounding vegetation and it> 
wet surfaces are accountable for the steady maintenance of these high 
humidity conditions is revealed in the trace shown in plate 24, figure A, 
which was taken in a tree top 38 feet from the ground and directly 
above the spot in which the trace in plate 25, figure B, was secured two 
weeks earlier. 

In similar fashion plate 24, figure A, exhibits the play of moisture 
conditions on a ridge within 500 yards of the location for plate 24, 
figure B. There was rain all day on Saturday and Sunday, giving the 
ridge the conditions of a ravine, but on the earlier days of the week 
fluctuations of humidity were recorded commensurate with those in the 
tree top. The ridges are exposed to air movements which prevent the 
attainment of the highest humidities and accelerate the drying of the 
natural evaporating surfaces of the forest. 

The trace shown in plate 26, figure A, exemplifies well the average 
conditions in Windward Slope forest, being intermediate between 
ravine and ridge conditions. The greatest fall in humidity, coming 
just at daybreak, is followed by either a sudden or a gradual rise which 
is continued through the night. 

The humidity conditions of the Leeward Slopes may be judged from 
plate 23, figure A, and plate 27, figure A. The former was taken in 
November in the physiological laboratory at Cinchona, a small building 
with windows and jalousies on all sides; the latter in April, in young 
ruinate near Cinchona. Both traces exhibit rapid and continuous 
fluctuations which carry the humidity to relatively low percentages 
during a large portion of the day. The laboratory and ruinate curves 
are comparable as respects the localities in which they were taken, but 
not as respects the months of the year, for the humidity conditions in 
November may be expected to exceed in every feature those of April 
(see fig. 1). 

Two traces have already been published 1 which go to show that the 

'Shreve, F. Studies on Jamaican HymenophyUacese. Bot. Gaa. 51 : L84-209. Mar. 1911. 



4l> A MONTANE RAIN-FOBEST. 

character of the daily humidity curve at Cinchona and in the ruinate 

is not entirely due to their position on the leeward side of the mountains 
but must be partly attributed to the fact that both of these localities 
have been deforested. The traces mentioned wen; taken at New 
Haven (lap, on the main ridge of the Blue Mountains, the first in a 
small clearing, the second in the Windward Slope type of forest which 
occupies the summit of the gap 200 yards distant. The former re- 
sembled the traces taken at Cinchona and in the ruinate; the latter 
showed a much more constant maintenance of high humidity, and 
resembled the curves for Windward Slope Forest. 

The records secured at Sir John Peak w r ere for the floor of an open 
stand of Podocarpus on the extreme summit (see plate 18). The 
curve from this location (plate 28, fig. A) is similar to that secured on 
the Ridge at 5,000 feet (plate 24, fig. A), that is to say, it exhibits a 
high and rather constant humidity on certain days those which are 
rainy or entirely cloudy and on other days shows depressions which 
are nearly as pronounced and long as those of the Leeward Slopes. 

EVAPORATION. 

The corrected readings of total weekly evaporation, which were 
secured in the open air just outside the laboratory at Cinchona and in 
two stations in the rain-forest, are exhibited in table 10. * There is, 
roughly speaking, an inverse relation between the weekly rainfall and 
the corresponding amount of evaporation. The highest weekly evapo- 
ration rates were 125.1 c.c. for the w r eek ending August 3, and 101 c.c. 
for the week of November 22, in both of which weeks there was an 
exceptionally light rainfall. The lowest weekly evaporation occurred 
in the first tw T o weeks of November, during a period of exceptionally 
severe precipitation. The average daily evaporation during the 
weeks of highest and lowest rate were respectively 17.9 and 1.8 c.c. 

The Ridge station was located in an open stand of Cyrilla, Tovomita, 
Ilex, and Clethra, and the atmometer was placed on the ground in such 
a position that it could be struck by the sun's rays during about half 
of the day, owing to the openness of the forest canopy. The weekly 
totals of evaporation for this station ranged from a maximum of 41.3 c.c 
to a minimum of 5.8 c.c, the rate in the former case being slightly 

1 The atmometers used were calibrated by comparison of their rate of loss with that of a standard 
cup and with the loss from petri dishes. The Btandard used was Livingston's cup No. 405. The 
petri dishes were of the standard size, 94 mm. in diameter, and were filled to within 3 mm. of the 
rim. The readings in terms of No. 405 may be 
converted into terms of standard No. 200 by 
multiplying by 0.82. The following figures show the 
coefficients of correction of the cups used, column A 
being the original coefficients determined at Tuc- 
Bon, B the coefficients determined at Cinchona in 
July, C those determined at Cinchona in August, D 
those at Cinchona in November, and E those found 
in Tucson after use. 



Cup 
No. 


A. 


B. 


C. 


D. 


E. 


Average 
of B. C, 












and D. 


294 




0.75 


0.84 


0.73 0.71 


0.77 


278 


0.55 


.69 


.72 


.71 .63 


.71 


287 


.56 


.69 




.72 


.62 


.71 


307 


.64 






.71 


.71 


.71 





; SHREVE 



Plate 23 




itrHSit^i-'-'"'" \m* ,1 



RELATION OF CONDITIONS TO HABITAT DISTINCTION^. 



47 



higher than that for the corresponding week at Cinchona, and that for 
the latter week being only one-twelfth that for Cinchona. 

The Ravine station was located at the spot shown in plate 1, in the 
dense shade of tree ferns, above which were growing Solatium and 
Gilibertia. The sun was rarety able to strike the atmometer, which 
was situated on the ground. The evaporation rate in the Ravine was 
constantly low, fluctuating only between 8.8 c.c. and 2.7 c.c. per week, 
or 1.2 c.c. and 0.4 c.c. per day respectively. 

Table 10. Rates of evaporation in the Cinchona region, July io Xovemher, 1909. 



Period ending. 


Rainfall, 
Cinchona. 


Evaporation. 


Cinchona, 
No. 294, 
No. 278. 


Ravine, 
No. 307. 


Ridge 
Xo. 297. 


July 20 , . 

27 
Aug. 3 

10 

17 

24 

31 
Sept. 6 

13 

20 

27 
Oct. 4.,, , 

11 

18 

25 

Nov. 1 

S 

15 

22 


cm. 
6.0 
2 

:s 

5.0 

l.S 

7.4 
15.4 
10.4 
12.7 
19.7 

6.4 
24.3 

7.3 
22.3 

3.3 

114.7 

78.2 

1.9 


c.c. 
47.0 
58.0 

12.'). 1 
47.2 
62.3 

3s!3 
55.5 
62.3 
40.7 
35.4 
86.0 
74.8 
67.4 
25.0 
61.3 
16.7 
12.8 
101.7 


c.c. 

8.6 

8.8 
3.6 

G : 5 

4.0 
'J 7 
5 7 
4.1 

ii .:; 
3.0 


c.c. 

16.4 
25.6 

11.3 

37.0 

5.8 



The addition of the weekly totals of evaporation for all of the weeks 
in which simultaneous readings were secured at Cinchona and in the 
Ravine gives 715.6 c.c. and 52.7 c.c. respectively. Reducing the rate 
of loss in the Ravine to unity gives a value of 13.5 for Cinchona, the 
average difference between the evaporation in the two localities being 
slightly greater than the maximum fluctuation of weekly rate at 
Cinchona (1:9.8). The addition of the weekly totals for the period 
in which atmometers were running at all three stations simultaneously 
gives amounts as follows: Cinchona 319.3 c.c, Ridge 120. 1 c.c, Ravine 
21.8 c.c. Reducing these amounts to terms of the Ravine as unity 
gives the following relative values: Cinchona 14.5, Ridge 5.7, Ravine 
1.0. A value in this series for the Windward Slopes would probably 
fall between 3.0 and 4.0, which would mean that the total evaporation 
of the Leeward Slopes at Cinchona is from four to five times as gr 
as that of the Windward Slopes in the vicinity of Morce's Gap. 



18 a ,\m\ iam; b UN-forest. 

Fn>m the four months' record of evaporation at Cinchona it ie 
possible to make a rough calculation of the total evaporation of the 
year. The atmospheric humidity is the most important climatic ele- 
ment in determining evaporation rate in the Blue Mountain region, 

and the average humidity for the four months from August to November 
is nearly the average for the year (84.9 as against 84.1 per cent). Tin- 
total annual evaporation may therefore be estimated as not far from 
three times the amount for the months covered by the accompanying 
readings. The total of the readings is 989.1 c.c., which may be placed 
at 1,000 c.c. for the present purpose. The total annual evaporation 
of 3.000 c.c. must be multiplied by 0.70, the factor by which the loss 
of the cup is reduced to terms of the loss from a free-water surface in 
a petri dish. The annual total is thus made about 2,250 c.c, again 
keeping the calculation in round numbers. The diameter of the petri 
dish is 94 mm., and the annual loss from its water surface per square 
centimeter would be 32.6 c.c. The average annual rainfall at Cinchona 
is 106 inches, or 271 cm. The total annual fall of rain per square 
centimeter is therefore 271 c.c, which is to 32.6 c.c. as 8.3 is to 1. 
The rainfall at Cinchona is therefore about eight times as great as the 
possible evaporation. Since the evaporation at Cinchona was found 
to be about fourteen times as great as that in typical Windward Ravine, 
the ratio of evaporation to rainfall for the latter locality is 1:112, if 
we take no account of the higher rainfall which undoubtedly exists on 
the windward side of the Blue Mountains An accurately determined 
ratio of evaporation to rainfall for this extremely hygrophilous habitat 
would probably be near 1 : 140. 

AIR TEMPERATURE. 

Reproductions of some of the thermograph traces secured at Cin- 
chona and in different natural habitats are shown in plates 23 to 28, 
and a digest of the data given by these curves is presented in table 11. 
Although no two of the thermograph traces are strictly comparable in 
the sense of covering the same interval of time, they serve to show the 
character of the daily march of temperature, and to emphasize the 
constancy of the temperature conditions not only throughout the day 
but throughout the several habitats in which they were secured. Only 
at Cinchona and in the Ruinate on the Leeward Slope was the average 
maximum temperature above 70 F. On Sir John Peak the average 
maximum was 60.5 F., which is higher than that of the Windward 
Ravines over 1,000 feet lower in altitude, and identical with the maxi- 
mum secured for Ridge forest at the lower altitude. The minimum 
temperature at Sir John Peak is, however, carried somewhat lower 
than that of Windward Ravines at lower elevations, in spite of the 
records on the peak having been secured later in the spring than those 
in the Ravines. 



SHREVE 



Plate 24 




RELATION OF CONDITIONS TO HABITAT DISTINCTIONS. 



49 



The average daily range of temperature is greater at Cinchona and 
in the Ruinate than it is in any of the forested areas. The Ruinate 
record was secured in an exceptionally clear and warm week, and its 
daily mean range probably represents the maximum for the entire 
region. The daily range at Sir John Peak, 11.3 F., is higher than for 
any other forested habitat, as might be expected. The Windward 
Ravines exhibit the lowest ranges of temperature, and those of the 
Slope, the Ridge, and the forest canopy are greater and of about the 
same order of magnitude. 

Table 11. Recapitidation of temperature data for different habitats. 



Location. 


Eleva- 
tion. 


Week 
ending 


Plate 
show- 
ing 
graph. 


Air temperature. 


Cinchona, 15-year 
averages for corre- 
sponding month-. 


Average 
maxi- 
mum. 


Average 

mini- 
mum. 


Average 
daily 

ran 


Maxi- 
mum. 


Mini- 
mum. 


Range. 


Cinchona 

Windward ravine . 
Windward ravine . 
In top of tree. . . . 
Windward slope . . 
Ridge 


feet 

5,000 

4,950 

4,750 

4,950 

4,950 

5,000 


Nov. 12 
Feb. 4 
Mar. 18 
Feb. 18 
Mar. 11 
Feb. 25 
Apr. 8 
Apr. 30 


23-1 
25-2 
24-2 
25-1 
26-1 
24-1 
27-1 
28-1 


F. 
72.2 
57.3 
59.8 
61.2 
61.3 
60.5 
72.0 
60.5 


F. 
58.3 
52.0 
52.7 
52.4 
51.9 
52.7 
51.3 
49.2 


13.9 
5.3 
7.1 
8.8 
9.4 
7.8 
20.7 
11.3 


F. 
68. 3 
67.0 
67.0 
67.0 
07.0 
67.0 
67 5 


F. 
57.3 
53.7 

53.9 
53.7 
53.9 
53.7 


F. 

11.0 

13.3 

13.1 

13.3 

13.1 

n . 3 

12.2 

12 






Sir John Peak. . . 


G.200 


67 . 5 





Such slight temperature differences are without significance in the 
differentiation of the habitats within the rain-forest, and are of impor- 
tance only in so far as they operate conjointly with other factors in 
affecting transpiration, growth, and other complex activities of plants. 
The low nocturnal winter temperatures of the highest peaks are suffi- 
ciently different from those of the slopes at 4,500 to 5,500 feet to be of 
significance in the limitation of species, as has already been suggested. 
In general, however, the role of temperature as a differential climatic 
factor in the Blue Mountain Region is an extremely unimportant one. 

SOIL TEMPERATURE. 

Six weekly graphs of soil temperature have, been selected from a 
larger number as exhibiting the most striking differences in this remark- 
ably uniform factor (plates 22 to 28). There is a close correspondence 
between the mean temperatures of the soil under the open sod of the 
lawn at Cinchona, in a coffee field with southerly slope and a light 
covering of weeds, and in the Ruinate (table 12). The substratum in 
Windward Ravines possesses a soil temperature nearly 1(T F. lower 
than those just mentioned, and the soil on the summil of Sir John 
Peak, in the Ridge type of forest, is closely like thai of the Windward 



50 



A Mi \ I \\i: RAIN-FORES'] . 



Ravine. A graph of temperature was Becured in the midsl of a heavy 
mass of hepatics and mosses which was Berving as the substratum of 
a number of epiphyl ic orchids, 10 feel from the ground od a Windward 
Slope. Thifl epiphytic Bubstratum showed a less daily range of tem- 
perature than the air of the Bams situation during the same week 
(6.4 P. as against 9.4 F. I, and, as compared with the soil in the Wind- 
ward Ravine, it exhibited the same minimum and a higher maximum 
temperature. The mean daily range of soil tempera 1 lire is so slight in all 
cases as to be without significance. It is less than 2 F. in all habitats 
excepting the Ruinate, and is only 1.1 F. in the Windward Ravines. 
The investigation of the daily march of soil temperature was under- 
taken partly with a view to investigating the possible relation of the 
daily march < f soil temperature to the activity of hydathodes. The daily 

Table 12. Recapitulation of soil-lemperature data for different habitats. 



Location. 



Cinchona 

Windward ravine 

Epiphytic Bubstratum . 

Ruinate 

Coffee field 

Sir John Peak 







Plate 


Soil tempcrat 


ure. 


Cinchona, 5- 


Eleva- 
tion. 


Week 
ending 


show- 
ing 
graph. 


Average 
maxi- 


Average 
mini- 


Average 
daily 


year means 
for corre- 
sponding 






mum. 


mum. 


range. 


months. 


feet 






F. 


F. 


o p 


F. 


5,000 


Nov. 12 


23-2 


62.5 


60.9 


1.6 


62.6 


4,900 


.Mar. 4 


29-1 


54.0 


52.9 


1.1 


60. r, 


4,950 


Mar. 11 


26-2 


59.2 


52.8 


6. \ 


60 . 5 


5,000 


Apr. 8 


27-2 


59.7 


57.5 


2.2 


60. 1 


4,500 


Jan. 28 


29-2 


61.4 


59.7 


1.7 


61.4 


6,200 


Apr. 30 


28-2 


53.5 


52.2 


1.3 


60.4 



range of temperature was found to be so slight and the lag of the daily 
minimum to be so short that there is no warrant for considering the soil 
temperature to be of importance in the operation of these structures. 
Differences of as much as 10 F., such as exist between the forested 
soils of the Windward Ravines and the open slopes of the leeward side 
of the Blue Mountains, are great enough to play a slight role in the 
distribution of plants, and this difference is perhaps partly responsible 
for the occurrence of lowland species at higher elevations on the leeward 
than on the windward side. Aside from this greatest difference in 
soil temperature, the factor is of no importance in the differentiation 
of habitats nor in the explanation of plant activities, and its measure- 
ment is of relatively little value in this region. 



SHREVE 



Plate 26 




SHREVE 



Plate 27 




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Plate 28 




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Plate 29 







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' i 



SEASONAL BEHAVIOR OF RAIN-FOREST VEGETATION. 

The relative constancy of temperature in the Blue Mountain Region, 
together with the lack of a pronouncedly dry season, gives the peren- 
nial plants of the rain-forest continuously favorable conditions for 
vegetative and reproductive activity in so far as concerns these major 
factors of the climatic environment. During my two sojourns at 
Cinchona I became interested in the seasonal variations of activity in 
the native trees and shrubs, and made observations which collectively 
cover all months of the year excepting June. The resulting data 
exhibit a diversity of behavior which would not be expected on a 
priori grounds in a region of such climatic constancy. There is, 
however, a season of relative rest in both vegetative and reproductive 
activity from October until January. In these months there occurs 
a total or partial fall of leaves from a few species of trees, and a small 
total mass of growth and bloom in the woody vegetation as a whole. 
It is significant that the months named are the most rainy and the 
most heavily clouded months of the year, a consideration of far more 
importance than their slightly lower temperature. From February to 
September there is greater activity, and it is in these months that the 
divergent behavior of the various forms is manifested. There are 
several species in which the winter is not a season of growth rest, but 
greatly outnumbering them are the plants in which the spring and 
early summer are the time of greatest shoot and leaf formation. The 
increasing number of sunny days in the months which follow the close 
of the winter rainy season is equivalent to a much greater rise of 
temperature for the plants than is indicated by the thermometrical shade 
readings, and may well be responsible for an increased vegetative activity 
which wanes considerably before the advent of midsummer. 

Following are described the principal features of the seasonal behav- 
ior of the Blue Mountain vegetation. 

I found growth and blooming to go on continuously at all months of 
the year in a number of under-trees and shrubs, including the following : 

Piper geniculatum. Malvaviscus arborcus. 

Piper fadyenii. Heterotrichum patens. 

Ba'hmeria caudata. Oreopanux capitatum. 

Bocconia frutescens. Acnistus arboreacens. 

Dodoiuea angustifolia. Datura suaveokns. 

In Oreopanax capitatum there is a short check in activity in mid- 
winter. In Datura suavcolens blooming occurs at intervals of three to 
six weeks throughout the year, being sometimes followed by a complete 
fall of leaves. 

A few of the larger trees also continue their activity throughout 
the year: 

Ilex montana var. occidentals. Peychotaria corymboaa, 

.Solanum punctulatum. Miconia quadran^ularis. 



A MONTANE RAIN-FOREST. 

In certain forms growth and leaf formation are continuous, while 
blooming occurs at a definite season, as in 

Alchornea latifolia. Sciadophyllum brownei. 

Oestrum hirtum. Gilibertia arborea. 

Brunellia comocladifolia. 

In all these forms a check in growth may be noticed in flowering 
shoots. In a few trees which otherwise grow continuously there may 
Im- noticed a check to growth for some months during the maturing of 
fruit, owing to the inflorescence being terminal, as in Cithatexylum 
caudatum and M lamia rubens, both of which bloom in the autumn and 
mature fruit during the winter, thereby sharing in the growth rest of 
some trees which are not in fruit at the time. 

The winter rest is most marked in those trees which lose their leaves 
and remain bare for several weeks, which are: 

Rhamnus spha-rospermus. Viburnum villosum. 

Clethra alexandri. Viburnum alpinuru. 

Clethra occidentalis. 

Some trees of Clethra occidentalis retain a few of their leaves, while 
trees of Clethra alexandri are often bare for a week or two. Among the 
above, and the trees which cease growth but do not lose their leaves 
entirely, there are well-marked terminal resting buds, covered by scale 
leaves of thin texture. 

The trees which bloom between the last week of January and the 
end of May are the following: 

Podocarpus urbanii. Eugenia marchiana, February. 

Hedyosmum arborescens, January. Meriania purpurea, March and April. 

Myrica microcarpa, March to April. Miconia quadrangularis. 

Alchornea latifolia, March to April. Mecranium purpurascens. 

Acalypha virgata. February to May. Gilibertia arborea, May. 

Ilex obcordata. Gilibertia nutans, May. 

Turpinia oocidentalis, May. Garrya fadyenii. 

Rhamnus sphaerospermus, March to April. Vaccinium meridionale, Jan. to March. 

Haemocharis haematoxylon, Feb. to April. Cestrum hirtum. 

Cleyera theoides, January. Cestrum sp. 

Clusia havetioides. Viburnum villosum, Feb. to March. 

Eugenia fragrans, February. Viburnum alpinum, Feb. to March. 

In some of the above the flowers are borne on the wood of the season, 
more particularly in those which bloom late, after growth has had time 
to progress, as in Turpinia occidentalis, Gilibertia arborea, and Gilibertia 
nutans. Much more commonly the flowers are borne on the wood 
of the preceding season. In the majority of cases shoot and leaf growth 
are simultaneous with the growth and unfolding of the inflorescence, 
that is, both cease before the coming of summer. 

In trees of constant growth the leaf -fall is likewise constant, and it 
is difficult to determine the age of leaves at fall unless they are very 
short-lived. In Bo?hmeria caudata a calculation based upon the interval 
of time between the first appearance of successive pairs of leaves on 
a shoot and the number of pairs persisting on shoots showed the leaves 



SEASONAL BEHAVIOR OF RAIN-FOREST VEGETATION. 53 

to be from five to seven months old at fall. In other constantly grow- 
ing forms the leaves apparently range from seven to twelve months 
in duration. 

In the trees which have a marked vernal growth leaf-fall is contin- 
uous throughout the year in one, Cyritta rajcemiflora, and is gradual 
throughout the summer in Myrica microcarpa, Turpinia occidentalis, 
and Gilibertia arborea. In Vaccinium meridonale the leaf-fall follows 
immediately upon the reaching of mature size by the leaves of the next 
succeeding spring, and proceeds rapidly so as to be complete by the end 
of April. Yet on the flowering shoots, where new shoots and leaves 
are not formed, the old leaves persist, so that we have leaves of the 
year and leaves of the preceding year functioning side by side. In 
Podocarpus urbanii the leaves of the previous year frequently persist 
on certain shoots, although they rarely remain until the third year. 
With the exception, then of Vaccinium and Podocarpus not to men- 
tion the scale-leaved Juniperus barbadensis and Baccharis scoparia 
there are no trees in the Blue Mountains on which the leaves persist for 
much more than twelve months. Among the shrubs the species of 
Wallenia are the only forms with leaves of more than one year's per- 
sistence, but I am unable to state their length of life. 

The species which bloom during July and August are the following: 

Weinmannia pinnata. Eugenia biflora var. wallenii. 

Brunellia comocladifolia. Sciadophyllum brownei. 

Guarea swartzii. Lyonia jamaicensis. 

Mettenia globosa. Turpinia occidentalis. 
Cyrilla racemiflora. 

The forms flowering from October to December are: 

Xectandra patens. Palicourea crocea. 

Miconia rubens. Citharexylum caudatum. 

Clethra occidentalis. Baccharis scoparia. 
Rapanea ferruginea. 

In connection with the behavior of the native winter-deciduous 
species I have been interested to observe the periodic activities of 
several north temperate trees planted in the grounds at Cinchona. In 
the European Quercus robur definite resting buds are formed in the 
late summer but the leaves are not shed during the autumn are indeed 
persistent in part until the following May. The resting buds swell 
during December and January and new shoots may be observed here 
and there over the tree during the entire spring, flowers being also 
borne during this long period of irregular activity. lAquidambar 
styraciflua also retains its foliage throughout the winter, new shoots 
forming as early as February and continuing for two months, while 
there is a gradual fall of the old leaves. In Liriodendron tvlipifera 
growth and leafing are continuous through the summer and into 
October, but during the autumnal rains the leaves, old and new, are 
shed, leaving the tree bare until the middle of February. Flowering 
takes place during April and May. Taxodium distichum retains its 



54 A MONTANE RAIN-FOREST. 

winter-deciduous habit, losing its leaves in October, not to renew them 
until late February or early March. 

Here, then, is a group of four north temperate deciduous trees which 
have almost identical foliation and defoliation behavior when found in 
their natural ranges, but exhibit considerable diversity when brought 
into the climate of Cinchona. 

There is no locality on the globe which possesses a completely uni- 
form climate throughout the year, and consequently no locality in 
which vegetation fails to be subject to the influences of fluctuating 
physical conditions. When the climate of the Blue Mountains is 
contrasted with the climate of such a region as the eastern United 
States it is made to seem uniform, in spite of its small annual fluctua- 
tions. The vegetation of the eastern United States is correspondingly 
marshaled into a unison of seasonal behavior, while the plants of the 
Jamaican mountains show only a slight tendency to such a marshaling 
(as indicated by the predominance of spring flowering and growth) in 
accord with the slight changes of physical conditions from season to 
season. In short, the more striking the differentiation of the two or 
more seasons of the year in a given locality, the more striking is the 
unison of vegetative and reproductive behavior in the vegetation; the 
less pronounced the diversity of the seasons, the nearer does the vege- 
tation approach the appearance of unbroken activity, an appearance 
regarding which we still know little, and shall continue to know r little 
until the entire subject of periodic phenomena is attacked by experi- 
mental methods. 



RATE OF GROWTH IN RAIN-FOREST PLANTS. 

Our knowledge of the rate of growth of tropical plants is nearly 
confined to the results of measurements which have been made on 
leaves and stems of lowland plants in which the rates are conspicuously 
high. Lock 1 found a rate of elongation of 231 mm. per day in the 
shoots of the giant bamboo, Dendrocalamus, in Ceylon, and Maxwell 2 
observed a rate of 107 mm. per day in the growth of banana leaves. 
Schimper 3 measured the leaves of Amherstia and some other tropical 
lowland trees and found their rates of growth to be exceedingly rapid. 
Such high rates of growth have been tacitly credited to all tropical 
plants, although there are doubtless very many lowland forms in which 
the usual rates of growth are relatively slow, while slower rates are 
naturally to be expected in montane tropical regions. 

Only a few weeks of observation in the Cinchona region were nec- 
essary to convince me that the rates of growth in the native rain- 
forest vegetation are relatively slow, and that the physical conditions 
under which they exist are not such as would be conducive to rapid 
rates. I became interested therefore in the growth behavior of the 
vegetation, as a summation of the many and less easily measured 
fundamental activities of the plants, and made both observations and 
measurements with a view to increasing our knowledge of plant activity 
in a region which presents equable conditions of temperature and 
almost uniformly favorable conditions of moisture. 

Attention has already been called to some of the seasonal differences 
in growth activity which exist between the various species of the 
rain-forest. It is natural to anticipate differences of rate between 
plants in which growth is continuous and those in which it is taking 
place during only a few months or weeks of the year; and there are a 
few cases in which such differences exist. The growth of Gilibcrtin 
and Turpinia is confined to a few weeks in the late spring, and is one of 
the most rapid growth phenomena in the rain forest. In Cyathea 
pubescens and other tree ferns the formation of new leaves takes place 
during the winter and spring, and their elongation is the most rapid 
growth phenomenon that has come under my notice. The elongation 
of leaves in all terrestrial ferns is much more rapid than the rate of 
growth in the leaves of other herbaceous plants, and this is due to 
the seasonal character of the growth of fern leaves and to the reserves 
in the rhizones through which the rapid growth becomes possible. 

Marked branches of individual trees of several common species were 
kept under observation from February until May 1900, and with 
the exception of Gilibertia and Turpinia none e xhibited rapid growth . 

^ock, R. H. On the Growth of Giant Bamboos. Ann. Roy. Hot. Card. Peradeniya, 2, pt. -, 
August 1904. 

2 Max\vell, W. The Rate of Growth of Banana Leaves. Bot. < Yntrl>., t'<7 , 1896. 
3 Schimper, A. F. W. Plant Geography, Oxford Edition, 1903, i>. 218. 

55 



56 



A MONTANE RAIN-FOREST. 



On the shoots of Hedyosmum arborescens and of Podocarpua urbanii 
which were under observation do new leaves were formed, although 
the shoots were favorably situated as respects light and their position 

on the tree. In Clethra and Viburnum the leaves which appeared 

alter the mid-winter defoliation of the trees grew less rapidly than the 
leaves of Alchornea, which is in continual activity, and made in a week 
about the same increase in size that may be made in a single day by 
the leaves of a maple in the eastern United States in April or May. 

Owing to the slowness of shoot growth I have confined my measure- 
ments to leaves. During the spring of 1906, from February to May, 
I made determinations of growth rate in Baehmeria caudaia, Alchornea 
latifolia, Ckthra occidentalis, Tovomita (Clusia) havetoides, Pilea nigres- 
cens, and Cyathea pubescens. 1 Additional measurements were made 
in 1909, from Julv to October. The measurements at both times 
were commonly made at fortnightly intervals. 

Table 13. Maximum rates of leaf growth in rain-forest plants. 



When measured. 


Rates, mm. per day. 


Average. 


1900, February to May: 


3.86 4.40 

2.46 2.50 1.81 2.91 2.26 ... 

2.06 2.06 1.74 1.56 

1.26 .95 

.33 .46 .38 

32.7 48.9 49.4 37.2 

.43 .41 .43 


4.13 
2.38 
1.82 
1.10 
.39 
42.00 


Clethra occidentalis 


Tovomita havetioides 


Pilea nigrescens 


Cvathea pubescens.. 


1909, July to October 

(to September for Pilea): 

Pilea nigrescens No. 1 


Pilea nigrescens Xo. 2 


.20 .29 [ .42 

.43 .60 .57 .29 .34 .61 


Pilea nigrescens Xo. 4 




1.14 1.35 1.06 1.00 .93 ... 

3.57 4.71 4.S6 

.57 .50 .29 


1.10 

4.38 
.45 


Asplenium alatum (fronds) 



The growth of each leaf is at first slow, reaches a maximum at about 
one-fourth to one-half its mature size, and then falls to a much slower 
rate. The most rapid maximum rates that were discovered in the 
measurements of 1906 were 4.4 mm. per day for Boehmeria, 2.9 mm. for 
Alchornea, and 49.4 mm. for the unfolding leaves of Cyathea. The 
slowest maximum was for Pilea 0.33 mm. per day. The measure- 
ments of 1909 were made only on Pilea, Peperomia basellcefolia, and 
Asplenium alatum. The maximum rates for all leaves measured in 
1906 and 1909 are given in table 13. 

The fact that Pilea nigrescens is the commonest herbaceous plant 
on the floor of the rain-forest, ferns excepted, and the fact that it 
exhibited the slowest rate of growth of any of the plants brought 
under measurement, led me to make a more extended series of observa- 

^Shreve, F. Rate of Growth in the Mountain Forests of Jamaica. Johns Hopkins Univ. 
Circ. Xo. 195, March 1907. 



RATE OF GROWTH IN RAIN-FOREST PLANTS. 



57 



tions on it than on any of the other species. Plants of Pilea seldom 
exceed a height of 50 cm. (20 inches), and maintain a smooth green 
epidermis on their oldest stems. The leaves are opposite and com- 
monly reach a mature size of 40 to 60 mm. in length, and are approxi- 
mately half as broad as they are long. Two or three pairs of juvenile 
leaves may frequently be found on the lowest nodes of plants which 
have reached the usual size, such leaves being nearly orbicular and from 
8 to 15 mm. in diameter. The inflorescences of Pilea are axillary, and 
their existence and growth are found to have no retarding effect on the 
growth rate of the leaves by which they are subtended. 

All plants of Pilea on which growth measurements were made in 
1906 and in 1909 were situated on the floor of a Windward Ravine, 
and were selected with a view to securing plants of average size and 
full vigor. The maximum rates of elongation are given in table 13. 
The entire series of rates of growth has been grouped according to the 
length of the leaf at the beginning of each 
interval of measurement the first group com- 
prising the rates in leaves less than 10 mm. 
in length, the second those from 10 to 20 
mm. in length, and so on by 10 mm. inter- 
vals to 60 mm. The averages of the groups 
of rates give data for a curve of growth 
rate, from which it is possible to learn the 
mean rate of leaf growth at six successive 
stages in elongation. The averages are 
expressed in millimeters per day in table 14. 

From these rates of growth it is possible to determine the average 
length of time required for a leaf to reach its mature size. Leaves which 
attain a length of 40 mm. are 118 days old at maturity; those growing 
to 50 mm. in length may be as old as 168 days, while those reaching 
the maximum size at 60 mm. are probably 218 days old at full maturity 
of size. It is possible that some of the leaves of maximum size make 
a growth above the average rate throughout their development, and 
thus reach the mature size in more than 118 days and less than 168. 
It has been commonly found, however, that large leaves continue to 
grow at a very slow rate, and it is on the basis of the growth rate of 
such leaves that the computation of 218 days is made. 

The growth of a new pair of leaves begins at about the time thai 
the next pair below them are half grown. The plants on which measure- 
ments were made had from seven to twelve pairs of leaves. If the 
leaves of these plants are assumed to have readied half their mature 
size in sixty days, as would be the case if all leaves made the most 
rapid growth, the age of the plants may be roughly estimated at from 
fourteen to twenty-four months. Below the sixth or seventh aode 
from the tip it is a common thing to find that some of the leaves have 



Tab lb 


14. 


Length of 


Average 


leaf. 


growth. 


IN III. 


m m . 


to 10 


0.36 


10 20 


.38 


I'D 30 


.30 


30 40 


.28 


40 50 


.19 


50 00 


.18 



;,s 



A MOM. WE RAIX-FOREST. 



fallen. Those on the sixth node will have been about one year old 
at fall, and those which still adhere to the lower nodes may be of any 
age up to two years. The lowest of the larger leaves are quite com- 
monly covered with epiphyllous hepatics. 

A more exact measure of the growth of Pilea in terms of the size 
of the plant was secured by making a computation of the relation which 
was borne by the new to the old extent of leaf surface in two plants 
that were under fortnightly observation and measurement, from the 
middle of July to the middle of September. On the completion of the 
measurements of these plants their green weight was secured and their 
leaf area was determined by the method commonly used in transpira- 
tion experiments. In the first plant eight leaves were in course of 
growth from July to September, in the second plant twelve leaves. 
The area of all the leaves on each plant in July was determined by 
using the September area of all the mature leaves and an approximate 
area for the leaves which had grown. This approximation was made by 
considering each leaf as an ellipse, with the length and width in July 
as the axes. The actual areas in September, the calculated areas in 
July, and the amounts of growth are shown in table 15. The extent of 
new leaf surface was 9.0 per cent that of the old in the first plant and 
12.3 per cent in the second. In the lack of similar data for any other 
rain-forest species or for the plants of any other region I am unable 
to make any comparison of these figures with the performance of other 
plants. 

Table 15. Rate of leaf growth in Pilea nigrescens. 





Fresh weight 
of top. 


Total area, 
September. 


Growth in 
area. 


Area, July. 


Growth, as 

percentage 

of July area. 


Pilea No. 1 
Pilea No. 2 


grams 
11.74 
10.07 


sq. cm. 
236.7 
263.3 


sq. cm. 
19.6 
28.9 


sq. cm. 
217.1 
234.4 


p. cl. 

9.0 

12.3 



In size and habit Pilea nigrescens closely resembles Pilea pumila of 
the eastern United States. The plants of the former species which are 
from one and a half to two years old are scarcely larger than the plants 
of Pilea pumila which have grown from seed, germinating in late April 
or early May, and have reached mature size in July or August. In 
other words, the American species makes from six to eight times as 
rapid development as the Jamaican species. 

There is no mathematically exact reciprocal relation between the 
growth rate and average transpiration rate of the plants in which both 
of these phenomena have been studied ; indeed, it would be worth while 
to seek such a relation only after the use of more exact methods of 
growth measurement and more careful measurement of physical con- 
ditions. There is every reason to believe, however, that the low rates 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 59 

of growth exhibited by rain-forest plants are occasioned by low rates 
of transpiration and adverse conditions for photosynthesis, the former 
being due chiefly to the prevailing high humidities and the latter to the 
high percentages of cloud and fog. The fact that growth is slower in the 
montane than in the lowland regions of the tropics is not surprising, 
since, in addition to the factors mentioned, temperature differences also 
enter the complex in favor of more rapid growth in the lowlands. 

TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 

METHODS AND MATERIAL. 

The work reported in the succeeding pages was directed to an investi- 
gation of the amounts and behavior of transpiration in characteristic 
montane rain-forest plants. The object kept in mind in planning the 
experiments was to secure results that would at once contribute to a 
precise knowledge of transpiration in the plants of an extremely moist 
region, and at the same time elucidate some of the local features of 
plant distribution as related to the physical characteristics of the habi- 
tats which had already been under investigation. 

Through the use of atmometric observations I have been able to 
institute a strict comparison between series of transpiration readings 
taken at different times and between the conditions of the field and 
the laboratory. The securing of simultaneous readings of transpiration 
and evaporation makes possible also the comparison of transpiration 
amounts and behaviors in plants of widely separated localities, with a 
basis of accuracy which removes this subject from the limbo of con- 
troversy into which botanical literature has sometimes seen it descend. 

The work on transpiration comprised the determining of (a) the daily 
march of the rate of water loss under the natural conditions of a mon- 
tane tropical region, (6) the effect of high humidities and of darkness 
on the rate, (c) the comparative amounts of stomatal and cuticular 
transpiration in the slightly circularized and thin-walled leaves of 
rain-forest plants, (d) the behavior of stomata as affecting the rate 
of transpiration, (e) the comparative transpiration rate and transpira- 
tion behavior of different types of rain-forest plants as simultaneously 
measured, and (/) the daily march of the relative transpiration 1 rate 

The plants used in these experiments were Alchornea latifolia and 
Clethra occidentalis, two of the commonest trees in the rain-forest ; 
Dodoncea angustifolia, one of the commonest shrubs on the Leeward 
Slopes of the Blue Mountains; Peperomia bascllcrfolin, a thick-leaved 
herbaceous plant of the open Ridge forests; PUea nigrescent and Pep- 
eromia turfosa, characteristic herbaceous plants of the floor of the 
Windward Slopes, and Diplazium celMdifolium and Asplenium alatum, 

'The term "relative transpiration" is used in the sense in which it was employed by Livingston 
Carnegie Inst. Wash. Pub. 50) to denote the ratio of transpiration ti> evaporation. 



()() A MONTANE RAIN-FOREST. 

extremely hygrophilous ferns of the narrowest Windward Ravines. 
The five herbaceous species last named were chosen as being the most 
characteristic plants of the three habitats of the rain-forest which 

differ most pronouncedly in general moisture conditions, as well as 
being suited to t lie requirements of experimentation. 

In work witli Alckomea, Clethra, and Dodoncea only cut shoots were 
used, and the potometer method was required for measurement of their 
transpiration. The greater part of the work was done with potted 
plants of the herbaceous species, and by the method of weighing sealed 
pots. The material used in 1909 w r as potted two months in advance 
of my arrival at Cinchona, and kept in the shade of a row of bamboos, 
I was thereby supplied with a set of vigourous plants in normal condition. 

Nearly all of my experimentation was carried on in the physiological 
laboratory building of the Tropical Station at Cinchona, which is 
admirably suited for such a purpose. This building is about 12 by 24 
feet in size, provided with a deep wall table, above which the sides of 
the building are completely occupied with alternating glass windows 
and open windows provided with jalousies. The light conditions are 
practically like those of the floor of the forest, and the temperature 
and humidity follow the outdoor shade conditions of the Leeward 
Slope both quickly and closely. Plants subjected to continuous dark- 
ness were placed in a small closet under the wall table, which was made 
light-tight by using a double jacket of plant driers. The arrangement 
of the jackets was such as to provide ventilation, and the size of the 
closet was great enough to enable me to get inside it and thereby to 
assure myself of its darkness. A moist closet was used, which was 
made of window sash and placed next to one of the windows of the 
laboratory. Portions of its sides w r ere covered with plant driers, kept 
constantly wet, and its floor was covered with sphagnum moss. It 
was possible to keep the humidity of this closet between 90 and 95 
per cent without difficulty. 

The woody shoots used in transpiration experiments were in each 
case cut under water and allowed to stand in water from six to ten 
hours before use. The potted plants w^ere prepared for use by covering 
the pots with plastocene, over which was rubbed a thin coating of 
vaseline. The pots were not sealed at the bottom, but were placed 
in saucers for convenience in handling. A w r ater-tight joint w r as then 
made around the circumference of the base (see plate 21 B). This 
made it possible to use a potted plant a second time by removing it 
from the saucer, taking off the cardboard top (covered with plastocene), 
and giving it a "rest" of several days. 

The moisture of the soil in w r hich my potted plants were growing 
w r as not precisely determined in connection with the transpiration 
series in which they were run. The soil used had been made up in 
such a way as to be uniform for all the pots, and each group of pots 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 61 

1 nought into the laboratory for experimental use had been subjected 
t < t he same frequent rainfall. The soil in which the plants were rooted 
was, therefore, like that of the open, extremely moist, and the lowering 
of moisture content to which it was subjected by the plants during 
the course of any one experiment was too slight to be thought of as 
affecting the transpiration rate. Most series were run for two days 
without opening the sealed pots, but in several other cases the same 
plants were opened at the top and bottom, set outdoors for a few days, 
and then used again. 

For the short intervals of the transpiration experiments evaporation 
was measured by weighing a porous cup atmometer, mounted in a 
small glass jar (see plate 21 B). This method was more satisfactory 
than the use of a burette, not only because of its greater accuracy, 
but because it obviated the error due to the expansion and contraction 
of the water column of the burette at morning and night. 

The area of leaf surface was determined by making blue prints of 
the fresh leaves, cutting and weighing in the usual manner. The 
figures given for area of leaf surface are twice the area of the blue prints, 
except in the case of leaves coated at top or bottom. The total transpi- 
ration of a leaf is therefore divided equally, in calculation, between the 
upper and lower surfaces. 

All readings of transpiration in the following tables are given in terms 
of the loss in milligrams per hour from a square centimeter of leaf 
surface, and the evaporation amounts are reduced from the atmometric 
readings to losses per hour in milligrams from a square centimeter of 
free water surface. In plotting the diagrams the evaporation has been 
divided through by 4 or by 10, as is indicated on each curve, it being 
thereby possible to condense the diagrams. The readings given oppo- 
site each hour are for the period closing at that hour, and the length 
of the period is indicated by the hour given on the preceding line of the 
table. The first hour given in each table is that at which the series was 
set. In the diagrams the readings are plotted to the ends of the hours. 

The stomatal readings given in connection with several of the tran- 
spiration series were made by the method used by Lloyd in his work 
on Fouquieria. 1 The method was used in the maimer recommended 
by Lloyd, and the precautions mentioned by him were all taken, in 
order to give this means of direct stomatal observation a thorough 
test. Merck's absolute alcohol was used, and the supply bottle was 
kept free of moisture by introducing a considerable quantity of dehy- 
drated copper sulphate. Livingston and Estabrook" found that it is 
unnecessary to use absolute alcohol in the operation of this method, 
and that essentially identical results are secured with grades of alcohol 

'Lloyd, F. E. The Physiology of Stomata. Carnegie [net. Wash. Pub. 82, 1908. 
Livingston, B. E., and Estabrook, A. H. Observations on th<- degree of stomatal mo\ ement in 
certain plants. Bull. Torr. Bot. ( Hub 39 : 15 22, L912. 



62 A MONTANE RAIN-FOREST. 

as low as 90 per cent. Lloyd attributes the efficacy of absolute alcohol 
in the fixation of stomata to its rapid dehydrating power, and found 
that the presence of a layer of mesophyll cells beneath a piece of epi- 
dermis which had been treated to absolute alcohol affected the openness 
of the stomata. I have found the openness to be little affected by 
underlying pieces of mesophyll thin enough to permit measurement of 
the stomata above them. It would appear, then, either that grades 
of alcohol below absolute are sufficiently active in dehydration to fix 
the walls of the guard cells, or else that the principle involved in this 
method is not that from which Lloyd started in the development of it. 

My measurements of stomata have been made in microns and the 
averaged values for each reading are given in the tables. I have com- 
monly read 24 stomata in each preparation, and have found that two 
such series agree within 1 to 6 per cent, in spite of the variability of 
the openness to which I shall draw attention. The stomatal datum 
used in plotting is the square root of the product of length and width 
of the averaged readings. This gives a figure which is proportional 
to the diameter of a circle of the same area, and is used in conformity 
with Brown and Escombe's law of the static diffusion of gases. 1 

DAILY MARCH OF TRANSPIRATION. 

The daily march of transpiration has been ascertained for eight 
species: Alchornea latifolia, Clethra occidentalism Dodoncea anguslifolia, 
Pilea nigrescens, Peperomia turfosa, Peperomia baseUcefolia, Asplenium 
alatum, and Diplazium celtidifolium. This group of species is repre- 
sentative of the trees, shrubs, herbaceous flowering plants, and hygro- 
philous ferns of the rain-forest. The several days on which the deter- 
minations of transpiration march were made were somewhat unlike 
as respects weather conditions, but varied only slightly around the 
normal type of day that has already been described as characteristic of 
the region (p. 17). The principal feature of the daily weather condi- 
tions that impresses itself on the curve of transpiration is the hour at 
which the clearness of the early morning is terminated by clouds or 
floating fog from the main ridge of the Blue Mountains. The daily 
curve of evaporation is influenced by the same variable weather con- 
ditions, and its shape for a given day bears a rather constant relation 
to the daily curve of transpiration. 

The maximum transpiration for the day may occur as early as the 
period from 8 to 9 a. m., as is shown for Clethra and Alchornea in 
Experiment 1 (table 16, fig. 2), and for Dodoncea in Experiment 2 
(table 17, fig. 3). More commonly the maximum occurs between 
10 and 12 a. m., or is sometimes registered as late as 1 p. m. in two-hour 
readings taken so as to terminate at that hour (see tables 17, 18, 19 
and 20). On the days which remain permanently or intermittently 
cloudy after the first obscuring of the sun, the transpiration shows a 

'Brown, H. J. and Escombe, I. Static Diffusion of Liquids and Gases in Relation to the 
Assimilation of Carbon. Phil. Trans. Roy. Soc. London, 193 : 283-291"; 1900. 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



63 



single pronounced maximum, while the recurrence of sunshine is 
frequently responsible for a second rise and sub-maximum (Experi- 
ments 2 and 3). The occurrence of a sub-maximum before the actual 
maximum of the day is rare. A slight increase of the evaporation rate 
in the early afternoon may be accompanied by a relatively pronounced 
increase of the transpiration, as occurred at 1 p. m. and 3 p. m. in Exper- 
iment 3. The later in the afternoon such secondary maxima of evap- 
oration occur, the less is the response of the transpiration rate: such a 




Mill III 



Fig. 2. Daily march of transpiration in ('lilhra (TC) and Alchornea (TA), together 

/"FT* 

with concurrent rate of evaporation (..) . rates of relative transpiration for the 

rp/-i rp 4 

two plants, and = respectively, and schematic depiction of weather conditions. 
E E 

maximum in Experiment 3 at G p. m. affecting neither Pilea nor Peperomia 

(table 18, fig. 4); slight secondary maxima in Experiment 2 affecting 
Dodoncea slightly on the first day of the experiment and not at all on the 



li! 



A MONTANE RAIN-FOREST. 



second; a secondary maximum in the late afternooD of the third dayof 
Experiment 4,a1 6 o'clock, having a positive effect on the rate of Peperomia 
baseUcefolia, causing checks in the rate of fall of Asplenium, Diplazium, 
and Peperomia turfosa, and failing to affect Pilea nigrescens. Very 
pronounced rises of evaporation in the night are frequent at Cinchona 
because of the nocturnal winds, and these rises are frequently accom- 
panied by slight increases of transpiration, as may be seen in the case 
of DodoncBa I Experiment 2. table 17, fig. 3) at 8 and '.) p. m., and in the 
case of live species under simultaneous investigation (Experiment 5, 
table 20, fig. 6) at midnight. The nocturnal rates of absolute transpira- 
tion, as compared with the diurnal, are not usually very low. An ex- 
amination of the curves for five species run through the 24 hours 
(Experiment 5, table 20, fig. 6) shows that the lowest nocturnal read- 
ings were related to the highest diurnal readings as indicated by the 
following percentages: Diplazium, 44 per cent; Asplenium, 40 per cent ; 
Pilea, 30 per cent; Peperomia turfosa, 20 per cent; Peperomia basel- 
lo?folia, 21 per cent. In Experiment 4 (table 19, fig. 5) the first reading 
taken in the morning on the first and third days of the experiment 
was an all-night reading, and its amount, determined at 6 a. m., may 
be compared with maximum rate for one day, which was abnormally 
low on the first day, but normal on the third. On tables 23, 24, and 25, 
the all-night readings of transpiration are indicated, and their amounts 
may be compared with the diurnal amounts for a number of experi- 
ments with three species, and about the same relation will be found 
to hold between nocturnal and diurnal rates as is indicated by the 
above percentages, although occasional very low nocturnal rates are 
registered. 

Table 16. Transpiration of Clethra occidentalis and Alehornea lalifolia. 

Experiment 1. Series run in open air with severed shoots, by potometer method. 
Clethra, 9 leaves, area 234.5 sq. cm.; Alehornea, 13 leaves, area 376.9 sq. cm. 













Clethra. 


Alehornea. 


Day of 
month. 


Hour. 


Temp- 
erature. 


Humidity. 


Evapo- 
ration. 








T 




T 












T 


E 


T 


E 


Feb. 2.... 


4 a.m. 
5 


56 
51 


73 

94 


3.20 








0.23 


0.072 


0.18 


0.056 




6 


55 


70 


6.20 


.30 


.048 


.16 


.020 




7 


55 


73 


3.60 


1.26 


.351 


.13 


.036 




8 


60 


53 


9.40 


' 2.43 


.257 


2.48 


.263 




9 


62 


67 


16.20 


2 . 78 


.172 


.' 84 


.175 




10 


67 


69 


10.50 


| 2.56 


.244 


1.48 


.141 




11 


59 


90 


6.80 


' 1.59 


.235 


1 . 16 


.171 




12 p.m. 


60 


90 


3.30 


.74 


.226 


.55 


.166 




1 


61 


93 


2.10 


.40 


.190 


. 34 


.156 




2 


60 


92 


2.70 


.49 


. 1 82 


.26 


.096 




3 


63 


90 


4.10 


.67 


.163 


.49 


.119 




4 


59 


92 


4.90 


.82 


.168 


.60 


.121 




5 


59 


91 


1.90 


.51 


.271 


.27 


.139 




6 


58 


90 


1.30 


.22 


.169 


.11 


.085 




7 


55 


92 




.06 


.... 


.05 


.... 




8 


55 


91 




.03 




.02 






9 


56 


88 




.02 




.01 






10 


55 


89 


1.20 


.02 


.012* 


.01 


.008 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



65 



Table 17. Transpiration of Dodonaia augustifolia. 

Experiment 2. Series run in open air, excepting from 2 to 5 p. in., February 28, by weighing 
method. Plant had 43 leaves, area 147.9 sq. cm. 



Day of month. 


Hour. 


Temp- 
erature. 


Humidity. 


Evapo- 
ration. 


T 


T 
E 


Feb. 27 
Feb. 28. ... 












G a.m. 


65 


90 




0.11 






4 


68 


80 




.20 






8 


64 


61 


4.30 


1.35 


0.314 




9 


69 


63 


7.40 


5.61 


.758 




10 


65 


85 


11.50 


3.89 


.338 




11 


65 


77 


6.20 


2.42 


.390 




12 p.m. 


66 


80 


3.60 


2.64 


.731 




1 


65 


78 




3.95 






2 


67 


80 


4.00 


1.62 


.405 




3 


67 


75 


7.20 


2.12 


.291 




4 


63 


80 


10.00 


2.23 


220 




5 


59 


90 


6.90 


1.24 


.180 




6 


57 


70 


6.50 


1.00 


.154 




7 


57 


42 


13.00 


1.02 


.078 




8 


56 


40 


22.60 


1.62 


.072 




9 


57 


52 


24.50 


1.48 


.061 




10 


55 


60 


15.10 


.77 


.050 


Mar. 1 


6 a.m. 


56 


88 


6.77 


,58 


.085 




7 


58 


87 




.43 






8 


65 


70 


5.50 


2.39 


.435 




9 


67 


64 


10.40 








10 


64 


54 


12.90 


9.42 


.730 




11 


74 


48 


17.70 


11.08 


.626 




12 p.m. 


79 


49 


19.10 


9.56 


.500 




1 


79 


43 


21.90 


10.57 


.482 




2 


71 


62 


22.00 


7.30 


.331 




3 


62 


73 


13.40 


6 . 52 


.486 




4 


66 


83 


15.10 


5.37 


.355 




5 


63 


86 


6.60 


2.30 


.348 




6 


59 


89 


3.80 


.51 


.135 




7 


59 


93 


2.30 


.67 


.293 




8 


57 


95 


1.00 











Table 18. Transpiration of Pilea nigrescent and Peperomia turfosa. 

Experiment 3. Series run in laboratory, with potted plants, by weighing method. 
Areas: Pilea, 110.9 sq. cm.: Peperomia, 55.3 sq. 



cm. 



Day of 
month. 


Hour. 


Temp- 
erature. 


Humidity. 


Evapo- 
ration. 


Pilea. 


Peperomia. 


T 


T 

E 


T 


T 

i: 


July^23 ... 
JulyJM... 


9 p.m. 
5 a.m. 


66 
61 


68 

88 












7 . 68 


0.57 


0.075 


0.31 


O.Olo 




6 


61 


95 


4.08 


.31 


.077 


.36 


.089 




7 


62 


96 


4.08 


.56 


. L38 


.51 


.13 




8 


64 


90 


5.40 


,6fi 


.121 


.72 


.134 




9 


69 


79 


6.60 


.81 


.1.':; 


1.31 


.198 




10 


73 


71 


11. 64 


1.49 


,128 


1 . !'. 


.127 




11 


75 


79 


8 34 


1.34 


.161 


1 . 24 


.11-. 




12 p.m. 


75 


83 


7.92 


1.31 


.166 


1 . 24 


. 157 




1 


71 


85 


8.46 


1.44 


.171) 


1.43 


.1 




2 


75 


92 


6 72 


1 1\ 


.184 


.96 


.111 




3 


-.1 


90 


7.68 


1.06 


.138 


1.13 


.1 17 




4 


70 


93 


r, B8 




.116 


. 77 






5 


69 


96 


6 "i 


.67 


.132 


.89 


.077 




6 


66 


98 


5 . ss 


.56 


.096 




.05:5 




9 


82 


98 


4.23 


.43 


.101 


22 


.051 



GO 



A MONTANE RA1N-FOKEST. 



Table 19. Simultaneous transpiration of five species. 

(Set A.) Extluimknt 4. Series run in laboratory, at three intervals, with potted plants, by weighing method. 
Areas: Pilea, 120.5 sq. cm.; Peperomia turfosa, 98.8 sq. cm.; Peperomia bw-lhrfolin, 103.9 sq. em.; Diplazium, 
321.5 sq. cm.; Asplcniinn, 192.7 sq. cm. 



Day of 

Month. 


Hour. 


Tem- 


m 
it 


id- Ev , ap - 
ration. 


Pilea 
nigrescens. 


Peperomia 

turfosa. 


Peperornia 
basellu'folia. 


Diplazium 
celtidifolium. 


Asplcnium 
alatum. 


ture. 


T 


T 

E 


T 


T 
E 


T 


T 

E 


T 


T 

E 


T 


T 
E 


Oct. 6. 
Oct. 7. 


9 p.m 

6 a.m 


60 


< 
























)5 5.23 


0.19 


0.037 


0.17 


0.033 


0.09 


0.018 


0.52 


0.099 


0.58 


0.112 




9 


62 


< 


)6 3.40 


.25 


.074 


.27 


.079 


.16 


.047 


.37 


.109 


.53 


.156 




12 p.m 


63 i 


)2 3.40 


.41 


.119 


.39 


.116 


.18 


.052 


.53 


.156 


.73 


.214 




3 


62 < 


)5 4.07 


.36 


.088 


.38 


.093 


.20 


.049 


.45 


.112 


.63 


.156 




G 


61 I 


)5 6.23 


.42 


.067 


.33 


.052 


.17 


.027 


.56 


.090 


.80 


.128 


Oct. 11. 


7 a.m 

9 


63 < 
70 i 


>2 






















S9 3.07 


.34 


.111 


.21 


.068 


.18 


.059 


.52 


.169 


.84 


.274 




11 


73 i 


S3 12.00 


.76 


.051 


.76 


.062 


.58 


.048 


1.12 


.093 


1.56 


.129 




1 p.m 


72 i 


>3 16.12 


1.09 


.067 


.92 


.057 


.67 


.041 


1.43 


.089 


1.81 


.112 




3 


69 I 


>9 15.52 


1.03 


.066 


.87 


.056 


.48 


.031 


1.25 


.080 


1.56 


.101 




5 


67 < 


>0 11.02 


.57 


.052 


.50 


.046 


.25 


.023 


.87 


.079 


1.23 


.112 




7 


64 < 


>3 5 . 85 


.26 


.044 


.15 


.026 


.20 


.035 


.44 


.076 


.64 


.109 




9 


63 < 


)2 4.27 


.19 


.045 


.32 


.074 


.17 


.039 


.42 


.097 


.63 


.147 


Oct. 15. 
Oct. 16. 


9 h 30 m p.m. 
6 a.m 






























6.36 


.23 


.036 


.21 


.033 


.23 


.035 


.70 


.111 


1.02 


.160 




8 








4.50 


.19 


.042 


.13 


.028 


.06 


.014 


.42 


.094 


.66 


.147 




10 








11.77 


.79 


.067 


.77 


.066 


.56 


.047 


1.17 


.099 


1.43 


.122 




12 p.m 








23.01 


1.58 


.068 


1.48 


.064 


1.25 


.054 


2.32 


.100 


2.41 


.105 




2 








16.20 


1.05 


.064 


.78 


.048 


.61 


.038 


1.56 


.098 


1.92 


.118 




4 








13.95 


.73 


.052 


.39 


.028 


.24 


.017 


1.01 


.072 


1.30 


.093 




6 








16.72 


.33 


.019 


.37 


.022 


.32 


.019 


.93 


.055 


1.15 


.068 




9 







7.80 


.19 


.024 


.10 


.013 


.13 


.017 


.64 


.082 


.86 


.111 


Oct. 17. 


8 a.m 






8.52 


.18 


.020 


.14 


.017 


.12 


.014 


.54 


.063 


.73 


.086 



Table 20. Simultaneous transpiration of five species. 
(Set B.) Experiment 5. Series run in laboratory with potted plants, by weighing method. Areas: Pilea, 106.0 
sq. cm.; Peperomia turfosa, 113.6 sq. cm.; Peperomia basellcefolia, 113.3 sq. cm.; Diplazium, 220.0 sq. cm.; 
Asplenium;, 380.8 sq. cm. 









Pilea 


Peperomia 


Peperomia 


Diplazium 


Asplenium 


Day of 
month. 


Hour. 


Evapo- 
ration. 


nigrescens. 


turfosa. 


basellaifolia. 


celtidifolium. 


alatum. 




T 




T 




T 




T 




T 








T 


E 


T 


E 


T 


E 


T 


E 


T 


E 


Oct. 29 
























8 


8.55 


0.51 


0.059 


0.22 


0.026 


0.27 


0.032 


1.01 


0.117 


0.81 


0.094 




10 


7.80 


.39 


.049 


.25 


.032 


.21 


.027 


1.03 


.132 


.80 


.110 


Oct. 30 


12 a.m. 


9.45 


.42 


.044 


.24 


.026 


.24 


.025 


1.27 


.134 


1.08 


.114 




2 


7.95 


.29 


.037 


.31 


.038 


.21 


.027 


1.13 


.142 


.94 


.118 




4 


7.05 


.28 


.040 


.22 


.031 


.17 


.024 


.99 


.141 


.88 


.127 




6 


8.32 


.33 


.039 


.34 


.041 


.15 


.018 


1.14 


.136 


.91 


.109 




8 


8.47 


.38 


.044 


.51 


.059 


.36 


.043 


1.32 


.156 


1.16 


.137 




10 


10.05 


.62 


.062 


.99 


.098 


.72 


.072 


1.99 


.197 


1.71 


.170 




12 p.m. 


11.92 


.74 


.066 


1.14 


.095 


.61 


.051 


2.25 


.189 


1.99 


.167 




2 


7.72 


.46 


.059 


.53 


.068 


.22 


.029 


1.17 


.151 


.91 


.118 




4 


6.00 


.47 


.078 


.29 


.047 


.15 


.025 


.91 


.152 


.94 


.156 




6 


7.05 


.41 


.059 


.46 


.065 


.21 


.029 


.97 


.136 


.80 


.113 


Oct. 31 


8 a.m. 


4.09 


.20 


.049 


.20 


.050 


.11 


.026 


.56 


.136 


.53 


.130 




10 


6.60 


.64 


.096 


.74 


.112 


.62 


.094 


1.53 


.232 


1.52 


.230 




12 p.m. 


9.97 


.82 


.082 


.88 


.088 


.48 


.047 


1.70 


.170 


1.65 


.082 




2 


6.82 


.47 


.069 


.48 


.070 


.13 


.019 


.97 


.142 


.94 


.251 




4 


7.35 


.49 


.067 


.52 


.070 


.21 


.029 


1.18 


.160 


1.13 j .154 




6 


6.97 


.52 


.074 


.51 . .072 


.21 


.030 


^.86 


.123 


.92 I .132 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



67 



Inasmuch as the absolute transpiration rate is of minor significance 
when considered independently of the concurrent rate of evaporation, 
the entire subject of the amplitude of the fluctuations of transpiration 
in each species, and the comparative rates of different species, will be 
taken up in the discussion of their relative transpiration rates. Suffice 
it to give here some of the extremes of absolute transpiration, con- 
sidered entirely apart from the rates of evaporation by which they were 
accompanied (table 21). 

Table 21. Extreme rates of absolute transpiration for unit time and area. 
Milligrams per hour per square centimeter. 



Plant. 


Maximum. Minimum. 


Clethra occidentalis 

Alchornea latifolia 

Dodonsea angustifolia 

Pilea nigrescens 


mg. 
2.78 
2.84 
11.08 
1.58 


mg. 
0.02 
.01 
.11 
.10 
.10 
.00 
.37 
53 


Peperomia turfosa 

Diplazium eeltidifolium .... 
Asplenium alatum 


1.75 
1.25 
5.11 

2.41 



Table 22. Comparative rates of transpiration and relative transpiration in five species. 



Transpiration amounts are the average hourly loss per square centimeter for the 

number of readings stated. 


Plants. 


No. of 
read- 
ings. 


Duration of readings. 


Total 
evapo- 
ration. 


Pilea 
nigres- 
cens. 


Pep- 
eromia 
turfosa. 


Pep- 
eromia 

lia.-cl- 
llsefolia. 


\ Dipla- 
zium 
eeltidi- 
folium. 


Asple- 
nium 
alatum. 


Set A.... 
Set A ... . 
Set A 

Set A 

Set B ... . 
Set B . . . 
Set B 

Set B 


5 

7 
9 

Avt 

5 

7 
G 

Av 


6 a.m. to 9 p.m. ; 8 a.m . 


4.465 

9.696 

12.093 


0.324 
.605 
.584 


0.308 
.533 
.485 


1 0.160 
.362 
.393 


0.488 

.866 

1.038 


! 0.655 
1.182 
1.278 


8.751 


.504 


.442 


.305 


.797 


1.038 


8 p.m. to 4 a.m 

6 a.m. to 6 p.m 


8.160 
8.507 
6.969 


.379 
.495 
.525 


.248 
.608 
.555 


.223 
.347 
.295 


1.085 
1.394 
1.134 


.915 
1.205 
1.117 


7.879 


.466 


.470 


.288 


1.204 


1.079 




ts A and B 


Averag 


;es of Se 


8.315 


.485 


.456 


.296 j 1.001 


1.059 


Set A 






.077 
.063 
.044 


.074 
.056 
.036 


.038 
.039 
,029 


.113 

.098 
.087 


.153 
.141 
.113 


Set A . . . . 








Set A. . . 








Set A 

Set B ... . 


Ave 








.0(11 


.056 


.036 


.099 


.136 














.046 
.068 

.073 


.030 

.(His 

.077 


.027 
038 

oil 


.133 

. L60 
.161 


.113 
.138 
.164 


Set B . . . 








Set B . . 








Set B 


Ave 








.059 


.05s 


.035 


.151 


.i.;s 


es of Sel 








.060 


.056 


.035 


. 1 26 


.137 









68 



A MONTANE RAIN-FOREST. 



Table 23. Amounts of transpiration an>l relative transpiration in Pilea nigrescens. 

Values Riven aro for eight seta of readings, all secured in laboratory by weighing method. 
Each individual plant is designated by letter. Starred readings are for intervals extending 
through the night. 



Hours. 


July 24. 


Aug. 6. 


Aug. 7. 


Sept. 18. 


Plant A. 


Plant A. Plant B. 


Plant C. 


Plant B. 


Plant D. 


Plant E. 


T 


T 
E 


T 


T T 
E 


T 
E 


T 


T 
E 


T 


T 
E 


T 


T 
E 


T 


T 

E 


6 

7 

8 

9 

10 

11 

12 p.m 

1 

2 

3 

4 

5 

fi 


*0. 570. 075 

.31 .077 

.56 .138 

65 121 
























*0.22 


0.113*0.10 


0.049 


*0.08O 






























.29 


.195 .21 


.143 


.10 


.0710.130.182 










.81 

1.49 

1.34 

1.31 

1.44 

1.24 

1.06 

.68 

.67 

.56 


.123 
.128 
.161 
.165 
.170 
.184 
.138 
.116 
132 














.65 


.213 


.44 


.143 


.42 


.136 


.30 .208*0.10 


0.080 


0.160.124 


.68 


.184 


.49 


.131 


.29 


.078 


.62 .207 


1.08 


.107 


1.35 


.133 


1.28 


.196 


.86 


.132 


.49 


.074 


.44 


.175 


1.08 


.070 


1.49 .097 


.68 


:i72 


.37 


.094 


'": 3 5 


.088 


.35 


.188 


.67 


.071 


.86 .098 


.096 


.45 


.141 


.28 


.091 


.17 


.052 


.27 .109 

















.64 


.063 


.88 


.087 


8 






.45 


.122 .24 


.067 


.22 


.060 






9 


.43 


.101 






.28 


.069 


















Hours. 


Oct. 11. 


Oct. 16. | Oct. 30. 


Oct. 31. 


Averages of 
T 
E 


Plant F. 


Plant F. ! Plant G. | Plant G. 


T 


T 
E 


T 


T 

E T 


T 
E 


-p T 
T i E 








i 






[Night:* 0.071 


6 ! 




*0.23 


0.0360.33 


0.039 




7 :::::: 












8 




.19 


.041 


.38 


.045 


*0. 200. 050 


} 8- 9: .116 


9 








0.340.111 


10 








.79 


.067 .62 


j .062 


.64 .096 


|10-11: .126 


11 








.75 .051 











1.58 


.068 .7S 


.066 


.82 .082 


|l2- 1: .121 
} 2- 3: .110 
J 4- 5: .101 
] 6- 7: .076 
} 8- 9: .070 


1 








1 09 


.067 








2 




1.05 


.064 


At 


.059 


.47 .069 


3 


1.03 


.066 


4 


.73 


.052 


.47 


' .078 


.49 .067 


5 


.57 


.051 


6 


.33 


.020 .41 


.058 


.52 .075 


7 


.26 


.044 


















I 


9 


19 


.045 .19 


.024 






| 

































TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



69 



Table 24. Amounts of transpiration and relative transpiration in Peperomia turfosa. 

Values given are for eight sets of readings, all secured in laboratory by weighing method. Each individual 
plant is designated by letter. Starred readings are for intervals extending over night. 



Hours. 


July 24. 


July 31. 


Oct. 7. ' Oct. 11. 


Oct. 16. Oct. 22. 


Plant A. 


Plant A. Plant B. 


Plant B. 


Plant B. 


Plant C. 


Plant D. 


Plant E. 


T 


T 
E 


T 


T 

T 

E L 


T 
E 


T 


T 
E 


T 


T 

T 

E X 


T 
E 


T 


T 

E 


T 


T 
E 


5 a.m. 

6 

7 

8 

9 
10 
11 
12 p.m. 

1 

2 

3 

4 

5 

6 

7 

8 

9 


*0.31|( 

.36 

.54 

.72 

1.31 

1.49 

1.24 

1.24 

1.43! 

.96 

1.13 

.77 

.39 

.32 


) 040 






















089 : 


1=0 31 044 *n i7n real 






*0.21 


0.033 












.133 
.134 
.19S 
.127 
.148 
.157 
168 










0.290.058 


0.330.067 


0.370. 


.23 .069 








.13 


.028 














.27 


.0800. o\ 


0.068 


": 6 5 


.105 


.66 



.106 


.88 


.141 


74 114 






.77 


.066 








.76 


.063 














.74 .118 39 .116 


1.48 


.064 .57 


.106 


.43 


.079 


.66 


.122 








.92 


.057 


.144' 
.147' 
.130 
.077 
.053 


.97 .131 






.78 


049 














.3b .093 


.87 


.056 




.20 


.067 


.35 


.118 


.36 


.121 




.39 


.028 






" 


.50 


.046 


















.33 .052 


.37 


.022 


.30 


.092 


.26 


.079 


.30 


.092 












.15 


.026 






























.22 


.051 










.31 


.074 


.10 


.013 


































Hours. 


Oct. 23. 


Oct. 24. 


Averages of 
T 
E 


Plant C. 


Plant D. 


Plant E. 


Plant C. 


Plant D. Plant E. 


T 


T 
E 


T 


T 
E 


T 


T 

E 


T 


T 
E 


T 


T 

E T 


T 
E 


5 a. m 

6 

7 

8 

9 
10 
11 
12 p. m 

1 

2 

3 

4 

5 

6 

7 

8 

9 


























Night:* 0.067 

I 8- 9: .0S6 
[lO-ll : .0S1 
12- 1: .096 
I 2- 3: .0S6 
[ 4- 5: .037 
[ 6- 7: .061 
\ 8- 9: .044 






































































*0.2 


0.078*0.29 


0.092 


*0.2/ 


'0.085 


*0.15 


O.OSS 


*0.14 


0.087 


0.150.090 



























.11 


.102 


.56 


.075 


.8c 


! .113 


1.71 


.106 


1.30 


.080 


1.75 


.108 












1" 
















.51 


.0S2 


.45 


.072 


.67 .108 


.97 


.072 


.78 


.05S 


1.25 


.093 




























.3c 


1 .07C 


.36 


.077 


.40 .086 


.38 


.041 


.26 


.028 


.65 


.071 
























1 














.48 


.078 


.027 


.is 


.028 













































70 



A MONTANE RAIN-1 < >KEST. 



TABLE 25. Amounts of transpiration and relative transpiration in Diplazium celtidifolium. 

Values are given f"r B6Y6D sets of readings, fill secured in laboratory by weighing method. 
Each individual planl in designated by letter. iStarrod re:iding3 aro for intervals extending 
over night. 



Hours. 


Oct. 7. 


Oct. 11. 


Oct. 16. J Oct. 30. 


Oct. 31. 


Plant A. 


Plant A. 


Plant A. 


Plant B. 


Plant B. 


T 


T 
E 


T 


T 

E 


T 


T 

E 


T 


T 
E 


T 


T 
E 


5 a.m. 

6 

7 

8 

9 
10 
11 
12 p.m. 

1 

2 

3 
4 
5 
6 

7 
8 
9 





















*0. 520. 099 






0.70 


0.1111 1 l 


0.136 

































.42 


.0941.32 


.156 


0.56 


0.136 




.37 


.109 


0.52 


0.169 






1.17 


.0991.99 


.197 


1.53 


.232 








1.12 


.093 




.53 


.156 


2.32 


.1002.25 


.189 


1.70 


.170 




1.43 


.089 










1.60 


.098117 


.151 


.97 


.142 




.45 


.111 


1.25 


.080 










1.01 


.072 


.91 


.152 


1.18 


.161 








.87 


.079 




.56 


.090 




': 9 3 


.055 


.97 


.136 


.86 


.123 




.44 


.076 














::::: 












.41 


.097 .64 


.082 
























Hours. 


Nov. 19. 


Nov. 20. 


Averages of 
T 
E 


Plant C. 


Plant D. 


Plant E. 


Plant C. 


Plant D. 


Plant E. 


T 

T 
1 E 


T 


T 
E 


T 


T 
E 


T 
T E 


T 


T 
E 


T 


T 
E 


5a.m. 
6 

7 

8 

9 
10 
11 
12p.m. 

1 

2 

.'! 

4 

5 

6 

4 

8 
9 
























I Night*: 0.115 

| 8- 9: .148 
jlO-11: .168 
]l2- 1: .152 
| 2- 3: .137 
| 4- 5: .116 
) 6- 7: .115 
} 9: .089 
























































1.120.125 


*1.22 


0.137 




0.79 0.149 


*0.90 


0.169 1-25 0.234 
















2.12 


.152 


2.38 


.171 




2.6S 


.171 


2.81 


.179 


3.46 9 21 








3.33 


.142 


3.74 


.158 





3.6C 


.144 


4.14 


.165 


5.11 


.204 




3.22 


.154 


3.43 


.164 


4. IS 


0.200 







































1.76 


.131 


1.64 


.122 


2.48 .184 






































































i 

















TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



71 




- 9 


p 










Q 


w 






U 




, > 


J 




sr* o 












* 


h 




r> O 


O 




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w-t 




- .a 






<J o 






5 u 







tj 3 


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i-i 


eJ 




ej 


h 




.. -a 


a 




8 


CQ 




~ V. 


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J* > 


cj 


^ 


-3 O 


*-* 


3 














- O 


> 




St 


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3 o 


d 


a 


3 *" 


6 


V. 

- 










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o 














04 


4 


> 




_ a 


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C 


M 

P .o 




c: 


- "--. 






3 g 


^3 


c 


S * 


a 


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tj ^ a^ 


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v. ^ 


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O 







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SHIW 



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Q 5 



72 



A MONTANE RAIN-FOKEST. 



INDIVIDUAL VARIABILITY OF TRANSPIRATION RATE. 

Several experiments were performed which gave simultaneous 
readings of the transpiration of two or three individuals of the same 
species. In each case the individual plants used were from the same 
spot in the rain-forest, were potted at the same time, and in every 
respect treated in the same manner up to the time of experimentation. 
The uniformity of soil-moisture conditions in the pots of the plants 
which I used for experimentation has already been mentioned. In 
spite of the apparent equivalency of the plants, and the fact that they 
stood side by side during the experiments, the rates of transpiration, 
when reduced to comparable areas, were found to differ to a considerable 
extent. On August 6 three plants of Pilea nigrescens were run in par- 
allel series and readings of their transpiration were taken simultane- 
ously. The plants were designated A, B, and C (see table 23) and their 
leaf areas were respectively 222 sq. cm., 326 sq. cm., and 360 sq. cm. 
On adding the hourly quantities of transpiration per square centimeter 
shown in table 23 the following totals are secured for the eight readings: 
A, 4.70 mg.; B, 2.99 mg.; C, 2.12 mg. 

On September 18 two plants of Pilea, D and E, were run simultane- 
ously (see table 23), and their areas were determined as: D, 427 sq. 
cm. ; E, 205 sq. cm. The total of the hourly quantities of transpiration, 
per unit area, for these plants is: D, 3.57; E, 4.74. 

On October 22, 23, and 24 three plants of Peperomia turfosa were 
run simultaneously. Their leaf areas and collective transpiration 
amounts per unit area are shown in table 26. 







Table 


26. 








Plant C. 


Plant D. 


Plant E. 


Area (in sq. ci 
Transpiration, 
Transpiration, 
Transpiration, 


n.) 




167 
2.01 
1.S4 
3.21 


129 
2.03 
1.66 
2.48 


227 
2.57 
2.17 
3.80 


October 22 
October 23 
October 24 











On November 19 and 20 plants of Diplazium celtidifolium (see table 
25) were run simultaneously, and the areas of leaf surface and the 
total transpiration amounts per unit area were as follows: 



Table 27. 



Plant C. Plant D 



Area (in sq. cm.) 445 

Transpiration, November 19 11 .55 

Transpiration, November 20 7.07 



454 
12.41 
7.85 



Plant E. 



363 
9.82 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 73 

The figures given for the three species indicate that all of them 
show variability in the amounts of their transpiration, sometimes slight, 
sometimes considerable. The fact that the plants in each series were 
placed side by side during the determination of their transpiration 
amounts, and were therefore under identical atmospheric conditions, 
together with the fact that the soil character and soil moisture were 
so nearly identical as to be incapable of exerting an influence on the 
available water supply, points to internal, physiological factors as 
causing the differences. There is evidence in the cases of Pilea and 
Diplazium that the plants which have smaller leaf area have higher 
transpiration totals, indicating a greater transpiration activity on 
the part of the smaller and younger plants. For Peperomia, however, 
these relations are reversed, at least on the second and third days, two 
plants of different area having almost identical totals on the first day. 

Such differences of behavior between plants of the same species under 
such nearly identical conditions is probably true of very many functions 
other than the transpiration. A row of plants grown in greenhouse 
or garden from the same seed, planted at the same time, with identical 
water supply and soil, will grow at different rates. Differences in 
growth rate and other activities may often be observed in plants grow- 
ing in their natural environment, although in the field it is always more 
difficult to be assured that the environmental conditions are so nearly 
equal as under glass or in the garden. Such differences of individual 
activity are an index of differences in the character or intensity of the 
many functions being performed by the plant, and may well be corre- 
lated with such differences in individual functions as have been shown 
to be true transpiration. There is apparently no definite specific 
rate of transpiration for the rain-forest plants investigated, although 
each species fluctuates around a normal rate for a given set of conditions 
and the limits of variability are different for different species. 

CONCURRENT RATES OF TRANSPIRATION IN DIFFERENT SPECIES. 
Several experiments were performed in which five plants of different 
species were run concurrently, with a view to ascertaining the degree 
of similarity or difference in their transpiration behavior under the 
same atmospheric conditions and to comparing the amounts of water 
loss from the different species; also, in view of the individual varia- 
bility of transpiration, to discover any possible changes in the relation 
of the species to each other as respects transpiration amount, in dif- 
ferent series of the same sort. The species used for these experiments 
were Pilea nigrescens, Pcperomia turfosa, Peperomia baseUcefolia, Diplar 
zium ccltidifolium , and Asplenium alatum, the habitat differences of 
which have already been mentioned. Two sets of the five species 
were used. The entire series of readings for Set A i> shown in table 19, 
those for Set B in table 20 (see figs. 5 and 6). 



74 



A MoNTAXK I; \IN-F()I!I>I . 



An examination of the curves in figure 5 will give a graphic concep- 
tion of the comparative behavior of the five species in Set A, on three 
in in-consecutive days, with progressively increasing evaporation. The 
curves for the five plants are such as to reveal the dominant influence 
of evaporation rate in controlling the transpiration. The water loss 
of Asplenium alatum tended to exceed one-tenth of the evaporation, 
area for area, throughout the three days, but exceeded it the least on 
the day possessing the highest evaporation. Diplazium celtidifolium 
ran considerably below one-tenth of the evaporation on the second day. 



2 40 



2.00 



1.60 



1.20 



.80 



-.40 



A.a. 
D.c. 
P.n. 
P.t. 
P.b. 

. 

10 





i i i r 




I i i : 



i i 



H A U. y 12 P It 



9 \ M n 1 P- M- 3 



6 A M 



Fig. 5. March of evaporation and of transpiration for five species during three days. The 
species are: Asplenium alatum (A. a.), Diplazium celtidifolium (D. c.), Pilea nigrescens 
(P. n.), Peperomia lurfosa (P. t.), and Peperomia basella folia (P. b.). Evaporation is 
plotted at one-tenth its scale value. 

but parallel it closely on the third, indicating that it is capable of 
withstanding an evaporation of 23 mg. per sq. cm. per hour the rate 
at 12 noon on the third day without evidence of wilting. The three 
species of lower transpiring rate than the ferns show a behavior in which 
they sustain approximately the same relation to each other during the 
three days, except for the tendency of the plants of lowest transpiring 
power to exhibit a relatively more rapid rate of increase with increasing 
evaporation. It is particularly true of Peperomia basellcefolia that its 
rate of w r ater-loss gradually approaches that of Peperomia turfosa on 
each of the successsive days. 

In the curves of figure 6 is exhibited the behavior of Set B of the 
five species under discussion. The evaporation runs slightly lower in 
this experiment than on the second day of the running of Set A, and 
the transpiration of Diplazium and Asplenium outruns one-tenth of it. 
The close correlation of the rates for all five of the plants with the rate 
of evaporation is quite as marked as in the case of Set A. The relation 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



75 



.y 



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a 



7(1 



A MOM AXE HAIN-FOKKM. 



of AspU nium and Diplazium with reference to each other is reversed, 
but the remaining species sustain about the same relation to each other 
and to the two ferns as in the preceding series. 

In table 22 arc given the average hourly amounts of transpiration 
for the five species, for each experiment with Set A and Set B. The 
nocturnal readings of Set B shown in figure 6 are separated from those 
of the following day in this table. 

"When the averaged readings of transpiration for the five species, 
during a series of periods in which all was subjected to the same 
evaporation conditions, are compared on the basis of the rate of the 
lowest one as unity, the following figures are secured, which may be 
designated the coefficients of transpiring power: 

Table 28. 



Species. 


Coefficient. 


Peperomia basellsefolia 


1.00 
1.54 
1.64 
3.38 
3.57 


Peperomia turfosa 


Pilea nigrescens 


Diplazium celtidifolium 





A close relation is here brought out between the character of the 
habitats occupied by these species and their coefficients of transpiring 
power. Peperomia basellcefolia is a plant of the xerophilous ridges, or 
a mid-height epiphyte, while Peperomia turfosa and Pilea nigrescens 
are found in the Slope and open Ravine forests, and Diplazium and 
Asplenium only in the most hygrophilous of the Windward Ravines 
(see coefficients for moist chamber, p. 104). 



RELATIVE TRANSPIRATION. 

The securing of the rate of evaporation concurrently with all transpi- 
ration readings has made possible the determination of the rate of 
relative transpiration the ratio of transpiration to evaporation. The 
ratios are determined by dividing the transpiration, in terms of the 
loss per hour per square centimeter of leaf surface, into the evaporation 
per square centimeter per hour from a free water surface. The trans- 
mutation of the atmometric readings of evaporation into terms of free 
water surface has been described on page 46. The relative transpira- 
tion figures are a true index of the transpiration rate as determined by 
the internal or physiological conditions of the plant and by the influence 
of light, in so far as its effects on the plant and the atmometer are 
different. The fact that all work here reported was done in the shade 
in conformity with the conditions of the rain-forest makes the error 
of relative transpiration figures due to light effects less than it would 
be in the case of experiments performed partly in the shade and partly 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 7 7 

in the sun, as would be the case under the natural conditions of the 
open. The figures for relative transpiration not only serve as an index 
of the changing physiological conditions of the plant (fluctuations of 
stomatal aperture, of water content of leaf, of vascular transfer of 
water, conditions of soil moisture, etc.), but they also make possible 
a strict comparison of the behavior of a species when investigated on 
different days. 

The usual daily course of the relative transpiration in all of the 
species investigated shows an early morning rise to a maximum which 
is earlier than the maximum of evaporation or that of transpiration 
and is usually the maximum of the relative rate for the entire day. 
In case the evaporation runs on to its maximum at a later hour than 
the maximum transpiration, or in case the two maxima coincide, it 
quite commonly happens that the relative rate reaches its maximum 
at an earlier hour than either. The fact that the rates of increase in 
evaporation and transpiration preceding their maximal points have 
been such that the rate of rise was greater for evaporation than the 
transpiration, causes a fall in the relative rate. Such fall is quite 
commonly followed in a few hours by a recovery, due to a pronounced 
fall in evaporation rate, accompanied by a less fall, of perhaps a rise, 
in the transpiration rate. The relative transpiration fluctuates during 
the mid-day and early afternoon in an irregular manner, sometimes 
reaching its daily maximum after the noon hour, but more commonly 
fluctuating below its morning maximum and finally falling in the late 
afternoon. The behavior of the rates for Alchornea and CUthra (table 
16, fig. 2) is typical for a large number of cases investigated on normal 
days. The curves for Pilea nigrescens and Peperomia turfosa (table 
18, fig. 4) show an even greater amount of mid-day fluctuation, and 
at 2 p. m. the former plant exhibits a maximum well above its early 
maximal point at 7 a. m. 

Figures 8, 9, and 10 have been drawn to show the character of the 
daily relative transpiration curves in several experiments with Pilea 
nigrescens, Peperomia turfosa, and Diplazium celtidi folium respectively. 
Each individual plant used in more than one series is designated by 
the same letter throughout. The actual rates upon which these curves 
are drawn may be found in tables 23, 24, and 25. The relative rates 
of all three of these characteristic rain-forest herbaceous plants are 
characterized by their uniformity, indicating a weak operation of the 
physiological regulations to which the inconstancy of the relative rate 
must be attributed. The maximum and minimum relative rates of 
these three species are shown in table 2!h 



7N 



A MliNTANK l; AIN-I Oh'KSI . 



n 



i^=j 



DWO 



c 


B 


- 






- 









a 









_ 












*- 






9 


B 






T3 


E 




I 

B 


> 


9 






a 


E 




- 




L 








9 






e 


h 




in 


u: 


( 




_ 








M 


g 


c 




E 




3 







a 


T> 


1 




^ 








d 


tj 


* 




u 








3, 


E 

5 




^ 


d 


> 


S 

s, 

At 


c 
o 

* 

C 





A 


u 

o 





s 


- 

B 


r. 


c 
1 

B 



c. 


1 


a 


O 


9 


1 




n 




c 


= 


in 
9 


- 
> 



< mo 



K O 



ce 



! 



* "2 T 

9 5 

T3 2 

> hO 

13 

OT Q lL 

3 o ^ 

a 

"** O 

JB S 

S< m 

a u 

Im oo O 

Mi <u ^ 

a 2 ^ 

.9 

&gi 

S M 

w ** 

in _ m 



'X 



t* .' n 



B 

> 

S '- < 



a 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



79 



In table 29 and fig. 11 are shown the mean daily relative transpiration 
curves of Pilea nigrescens, Peperomia turfosa, and Diplazium celtidi- 
folium, as determined respectively from the 84, 82, and 54 readings of 
tables 23, 24, and 25. There is a general similarity in the three curves, 







i i 



1 r 



i i 



i A v. 6 



10 11 12 1 



Fig. 10. Relative transpiration graphs for successive experi- 
ments with Diplazium cellidi folium. Each individual 
plant used is designated by the same letter throughout. 
(For values see table 18.) 

save for the tardy maximum of Peperomia and its low rate at the 4 p.m. 
and 5 p. m. readings. The rise of Diplazium at the 8 p. m. and 9 p. m. 
readings will be commented on later, in connection with its stomatal 
behavior. It may be observed here that the nocturnal relative rates 
are in no case as low as the lowest of the diurnal rates. 

Inasmuch as several of the experiments show that there is a' 'break" 
in the morning rise of relative transpiration, before the hour at which 
the maximum evaporation of the day is recorded, an indirect method 
was employed to determine whether a progressive increase of evapo- 
ration rate is attended by a definite behavior on the part of the relative 



80 



A MOM AM: RAIN-FOREST. 



transpiration. This was done in the following manner: The relative 
rates for the three plants exhibited in tables 23, 24, and 25 were grouped 
according to the rates of evaporation which prevailed during the same 
hours for which the relative rates were determined, and were grouped 
by increments of 1 milligram per square centimeter of water surface 

Table 29. Averaged daily march of relative transpiration in three species, together with 

maximum and minimum readings. 

Averaged from S2 readings for Pcperomia turfosa, S4 for Pilea 
ni{jrescens, and 5G for Diplazium celtidifolium. 



Time of dav. 


Peperomia 

turfosa. 


Pilea 

nigrescens. 


Diplazium 
celtidifolium. 


8 to 9 a.m 


0.086 


0.110 


0.148 


10 11 


.081 


.126 


.168 


12 1 p.m 


.096 


.121 


.152 


2 3 


.086 


.110 


.137 


4 5 


.037 


.101 


.116 


6 7 


.061 


.076 


.115 


8 9 


.044 


.070 


.089 


Night 


.067 


.071 


.115 


Maximum. . . 


.198 


.213 


.234 


Minimum 


.013 


.020 


.055 



.130 
.160 
.140 
.120 
.100 
.080 
.060 
.040 
0.20 




X 



I 



X 



NIGHT 



3-9 a. m 



10-11 12-1 pm- 



4-5 



6-7 



8-9 



Fig. 11. Mean daily course of relative transpiration rate for Diplazium, Pilea, 
and Peperomia turfosa, as averaged from graphs given in figs. 8, 9, and 10. 



per hour. The averaged relative rates were then plotted to evapora- 
tion. The resulting curves show the collective behavior of the several 
plants experimented upon, in the several series in which they were run. 
On account of the many fluctuations of the curves they were smoothed 
in groups of three, the average of each three readings being taken as 
the value of the middle one of the three. The smoothed curves are 
given as dotted lines in figure 12. Pilea shows a fall in relative rate 
which is irregular but progressive; Peperomia shows a remarkable rise, 



TRANSPIRATION BEHAVIOR OF RAIX-FOREST PLANTS. 



81 



followed by an abrupt fall, but the general trend of the smoothed curve 
is downward; Diplazium exhibits irregular behavior, but its smoothed 
curve also shows a slight tendency to drop. The number of readings 
on which the placing of the points in these curves is based may be seen 
in table 30 to be small in many cases. A very much larger number of 
readings of relative transpiration, under varying conditions of evapo- 
ration, would make possible the construction of curves much more 
nearly representative of the actual influence exerted by a rising evapo- 
ration rate upon the physiological controls of the leaf and plant. The 




0.50 



-l l 1 I l 1 I I 1 l l I l I I L I i : ! i I j i i i_ 




150 



.100 



0.50 



i ' i i i ' i i i i i ' ' ' i ' i 1 i 1 i : 1 1 l_ 



200 D.c. 



150 



KM 



0.50 




i i i i i i i i i i ' i ' l I l i 1 l l l 1 1 1 

(i l 2 3 4 5 6 7 8 9 1" 11 12 13 II IS 16 r. I Jl : , L' l::i '-'I 



Fig. 12. Graphs to show effect exerted upon relative transpira- 
tion rate by progressive increase of evaporation rate. Data 
secured for Pilea, I't j>< romia turfosa, and DipUuiwn (see 
taMes 1G, 17, and L8). Dotted lines are si ! values. 



S2 A MONTANE RAIN-FOREST. 

curves under discussion show a slighl genera] tendency toward a fall 

of relative rate with rising evaporation, but they fail to show a decided 
break in the relative Pate, unless the abrupt rise and fall of Pcperomin 
may be so interpreted. The evidence of these averaged curves is quite 
different from that of single curves and has the effect of swamping the 
possible differences of behavior in different individuals. The actual 
break in the rise of the relative rate may best be sought on the individual 
curves and is very conclusively shown in the several cases to which 
attention has already been called. The rarity with which the hourly 
evaporation rate for Cinchona rises above 16 mg. per hour may be 
inferred from the small number of readings in table 30 above that 
amount. The curves (in fig. 12) afford some evidence that the physio- 
logical controls which are operative in lowering the relative rate may 
have operated during the rise of the evaporation from about 5 mg. 
per hour to 16 mg., w r hile the further rises in relative rate shown for 
Pilea under 23 mg. of evaporation and for Diplazium under 20, 23, 
and 25 mg. doubtless represent the ratios derived from a water loss 
which is due in large measure to cuticular transpiration, and is bej^ond 
the retaining power of any of the normal controls of the plant. 

COMPARISON OF RELATIVE TRANSPIRATION RATES IN RAIN-FOREST 

AND DESERT PLANTS. 

Livingston 1 has determined the rates of relative transpiration for 
several desert annual plants, at the Desert Laboratory at Tucson, 
Arizona, and Mrs. Edith B. Shreve 2 has secured, at the same place, 
readings for Parkinsonia microphylla, a typical desert perennial, in 
plants of several ages and seasonal conditions. The possession of these 
readings, made by the same methods used in my own w r ork, makes 
possible a comparison of the amounts and limits of relative transpira- 
tion in plants of tw r o most w T idely unlike regions. The species used by 
Livingston are ephemerals, which complete their life cycle during the 
summer rainy period, and are typical desert plants in no respect except- 
ing the rapidity with which they grow and come to maturity. His 
experiments w r ere all made in the sun, but many of his minimum rates 
of relative transpiration were secured for nocturnal or partly nocturnal 
intervals. Parkinsonia microphylla is a perennial microphyllous tree, 
which passes a portion of the year in a leafless condition. The experi- 
ments of Mrs. Shreve w r ere made on small plants without leaves, and 
on the twigs of trees, both with and without leaves, as w r ell as on plants 
grow r n from seed under hot-house conditions. Her experiments were 
all performed in the sun with the one exception noted. It will be 
recalled that all of my own work w r as carried on in the shade, with the 
exception of that on Alchornea, Clethra, and Dodonaa. 

1 Livinston, B. E. The Relation of Desert Plants to Soil Moisture and to Evaporation. Carnegie 
Inst. Wash. Pub. 50, pp. 45-65, 1906. 

2 Shreve, Edith B. The Daily March of Transpiration in a Desert Perennial. Carnegie Inst. 
Wash. Pub. 194, 1914. 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



83 



The highest relative rates secured in the Jamaican plants were 0.758 
for Dodonoea among sun readings, and 0.274 for Asplenium alatum 
among shade readings. Among Mrs. Shreve's readings the highest 
was a shade reading of 0.818 in a hot-house plant, the highest in an 
outdoor plant being 0.353 for the branch of a tree in leaf. Livingston's 
highest readings were 0.785 for AUionia and 0.371 for Boerhaavia. In 
short, the highest of the sun readings in Jamaica, taken on one of the 
most xerophilous shrubs, nearly equals the highest of the sun readings 
taken by Livingston for AUionia, which is one of the many desert 
ephemerals unable to withstand periods of rainless, sunny weather 
for more than a fortnight. The maximum readings for Clethra and 
Boerhaavia are similar, being 0.351 and 0.371 respectively, and those 
for Alchornea and Tribulus happen to be identical: 0.263. A general 
parallel is thus established between the relative rates in the summer 
ephemerals of the desert and the most xerophilous of shrubs and trees 
in the Blue Mountain region. The maximum rates of relative trans- 
piration secured by Mrs. Shreve for Parkinsonia range, on the whole, 
lower, for all of her experiments performed in the sun, than the maxi- 

Table 30. Relation of relative transpiration to increasing evaporation. 

Relative transpiration readings for three speeies grouped according to the evaporation rate 
of the interval in which each transpiration reading was secured. The number of readings aver- 
aged in each group is indicated. 



Evapo- 


Pilea nigrescens. 


Peperomia turfosa. 


Diplazium 
celtidifolium. 














ration. 


Relative 


No. of 
readings. 


Relative 


No. of 
readings. 


Relative 


No. of 

readings. 




transpi- 
ration. 


transpi- 
ration. 


transpi- 
ration. 


">'.! 

















0.182 


1 




.... 




.... 


1 


.154 


4 












2 


.141 


3 





102 


3 






3 


.123 


17 




088 


G 


0.214 


3 


4 


.078 


6 




078 


9 


.132 


3 


5 


.102 


5 




091 


8 


.109 


1 


6 


.114 


9 




098 


14 


.155 


5 


1 


.OS.") 


6 




1 1 )5 


7 


. 132 


4 


8 


,097 


G 




1 58 


2 


.140 


2 


9 


. 1 182 


1 




046 


3 


.170 


1 


10 


.090 


5 








.197 


1 


11 


H7s 


4 




079 


3 


. 133 


3 


12 


.051 


1 




062 


1 


. L29 


1 


13 


.052 


1 




000 


4 


.139 


6 


14 
















15 


078 


3 




056 


1 


lt',7 


4 


16 


1 151 1 


3 




070 


6 


.()ss 


3 


17 




. 












is 
















19 
















20 












L72 


3 


21 
















22 
















23 


.068 


1 




06 l 


1 


i 3 ; 


3 


24 


.... 














25 


.... 


, 








171 


3 



M A MONTANE RAIN-FOREST. 

mum rates of Livingston for Tribulus, Allionia, and Boerhaavia. Also, 

my own relative rates for herbaceous species of the rain-forest flora, 
investigated in the shade, exhibit a lower range of maxima than do 
the plants used by Livingston. If, however, these rain-forest plants 
had been placed in the sun their relative rates would have mounted to 
much higher figures, because of their thin epidermis and light eutiniza- 
tion, taken together with the fact that the high humidity is deterrent 
to rapid evaporation even in the sun. A test made by placing a plant 
of Pilea nigrescens in full sunshine from 9 h 30 m to 10 h 30 m a. m. gave a 
relative transpiration rate of 0.238, which is twice as great as the highest 
shade rate secured for this species. The same plant was kept in the 
sun from 10 h 30 m to ll h 30 m (there being a few minutes of cloudiness 
in this hour), and the relative rate fell to 0.193, although the evapora- 
tion fell only from 22 to 21 mg. Other tests made in the sunshine 
with the more hygrophilous Asplenium and Diplazium showed them 
incapable of withstanding direct insolation for so much as one hour, 
and although the wilted condition of their leaves indicated a high water 
loss they were not weighed at the ends of the periods. 

The fact that the relative rate of Pilea in the shade was doubled by 
placing the plant in full sunshine gives at least some warrant for 
estimating that the relative rates of the other herbaceous species would 
be increased in the sunshine to double their shade values. If such 
approximate values for the relative transpiration in the sunshine be 
taken for the herbaceous plants of the rain-forest, they will be of the 
same general order of magnitude as Livingston's rates for the desert 
ephemerals, and both of these classes of plants will exceed, in general, 
the rates secured by Mrs. Shreve for Parkinsonia. 

The minimum rates of relative transpiration are extremely variable 
in any number of experiments w T ith the same species, and their signifi- 
cance in comparison is not so great as that of the maximum readings. 
The highest minimum rates found among the data which are under 
comparison are those of the hygrophilous ferns of the rain-forest, while 
the lowest of the rates for Peperomia basellcefolia are of the same general 
order of magnitude as those for the desert ephemerals and for Parkin- 
sonia (see table 31). 

It is possible to say, in summarizing, that the most nearly xerophilous 
of the rain-forest plants exhibit about the same maximum relative 
transpiration rates as do the most nearly hygrophilous of the desert 
herbaceous species. The relative rates for herbaceous plants of the 
rain-forest, as determined in the shade, are about half of the rates for 
the desert ephemerals, as determined in the sun, and there is some 
evidence that this difference is due to the fact that one set of experi- 
ments was performed in the sun and the other set in the shade. The 
rates for Parkinsonia, determined in the sun, are of about the same 
general order of magnitude as the shade rates for the Jamaican her- 
baceous species. 



TRANSPIRATION 7 BEHAVIOR OF RAIX-FOREST PLANTS. 



85 



In spite of the differences which exist between the maximum relative 
transpiration rates for the several rain-forest herbaceous plants and for 
the several species of desert ephemerals, when compared among them- 
selves, a general review of the readings for all of the widely divergent 
types examined in the work of Livingston, that of Mrs. Shreve, and 
in my own discovers a much greater uniformity in the amounts of 
relative transpiration than might be expected in view of the widely 
dissimilar anatomical characteristics of the plants and the sharply 
contrasted climates under which they exist. 

Table 31. Showing comparative values of relative transpiration for plants investigated 
at Tucson, Arizona, and at Cinchona, Jamaica. 





Maximum. | Minimum. 


At Tucson, Livingston's rates: 

Euphorbia, Experiment 1 

Tribulus, Experiment 4. . . 


0.070 
.263 
. 237 
. 785 
.371 


005 
008 
018 
054 
029 


Tribulus, Experiment 5 

Allionia, Experiment 6 




At Tucson, Mrs. Shreve's rates: 
Parkinsonia microphylla 
Leafless seedling, in sun. 
Do 




.213 
.136 
.151 
.158 
.353 
.168 
.459 
.S18 


084 
034 
049 
026 

007 




Leafless branch of tree, in sun .... 
Do 


Leafv branch of a tree, in sun .... 
Do 


Greenhouse plant, in sun 
Greenhouse plant, in sha< 




ie 




Maximum. 


Average. Mir 


imum. 


At Cinchona: 


0.351 
.263 
.758 
.119 


0. 

.... 

0.061 
. 059 
( I.",.-, 
.058 
.035 
.035 
.I)!' 1 .* 
.151 
.136 
.138 


012 

008 
050 
020 
037 
013 
026 
014 
(Ms 
<>.-,<; 
117 
068 
078 


Alchornea latifolia 




Peperomia basellaefolia, 4. 

Peperomia basellaefolia, B 

Diplazium celtidifolium, A.. . 
Diplazium celtidifolium, B. . . 

Asplenium alatum, B 


.096 

.116 
. 112 

.058 

.093 
. 169 
.232 
. _'7 1 
.251 





The total annual evaporation recorded at Cinchona is 32. G c.c. per 
square centimeter of free water surface; that at Tucson is 345 C.C. 
per square centimeter. 1 The two rates are in the ratio of 1 to 10.6. 

. T 

The higher rate of evaporation at Tucson means that in the ratio =7 

for that region the values for T must be ten times greater than the 

'Shreve, F. Rainfall as a Determinant of Soil Moisture. Plant World, 17 : 9 -26, 1914. 



Sli 



A M < > NT A N K H A I N-F< KEST 



values for T at Cinchona if a general equality of the ratios exists for 
the two regions, as lias been shown. In other words, the existence of 

a general equality of maximum relative transpiration between regions 
of widely diverse climatic conditions, ('specially with respect to the 
evaporating power of the air, indicates thai there is a rough relation 
of equality between the maximum transpiring power of the plants 
native to these regions and the evaporation conditions by which the 
regions are characterized. In a comparison, then, of the transpiration 
capacities of plants found in regions with graduated differences of 
evaporation conditions, it is possible that we may find the transpiration 
capacities falling into a parallel series of proportional differences. 

These statements are not at all in harmony with the commonly 
accepted view that the transpiration of desert plants is low as compared 
with that of plants in moist regions. As a matter of fact it is the 
transpiration of rain-forest plants which is low, and the transpiration 
of desert plants which is high, in terms of unit areas, and (for Cin- 
chona and Tucson) the rates are roughly proportional to the annual 
evaporation of the two regions: as 1 is to 10. The question of the 



Table 32. Influence on transpiration exerted by coating upper or lower leaf surfaces. 

Series run in laboratory, with three individuals of Pilca nigresctns, by weighing method. 
First group of readings on uncoated plants, second on plants coated as indicated. Leaf areas 
(top and bottom): A. 221.8 sq. cm.; B, 328.3 sq. cm.; C, 359.9 sq. cm. 



Date. 


Hour. 


Temp- 
erature. 


Humid- 
ity. 


Evapo- 
ration. 


Uncoated. 


Pilea A. 


Pilea B. 


Pilea C. 
























T 


T 
E 


T 


T 
E 


T 


T 

E 


Aug. 5. . 


9 h 00 m p.m. 


62 


90 
















Aug. 6. . 


6 00 a.m. 


59 


90 


1.98 


0.16 


0.081 


0.20 


0.099 


0.45 


0.227 




8 00 a.m. 


63 


85 


1.50 


.21 


.141 


.4:5 


.286 


.59 


.391 




10 00 a.m. 






3.06 


.83 


.272 


.88 


.286 


1.31 


.427 




12 00 p.m. 


73 .. 


83 


3.72 


.58 


.157 


.97 


.262 


1.37 


.368 




2 00 p.m. 


66 


90 


6.54 


.97 


.149 


1.73 


.264 


2.56 


.392 




4 00 p.m. 


65 


93 


3.92 


.69 


.177 


.74 


.189 


1.35 


.345 




6 00 p.m. 


63 


90 


3.16 


.33 


.105 


.57 


.181 


.89 


.282 




8 00 p.m. 


62 


90 


3.66 


.44 


.121 


.49 


.134 


.89 


.244 


Date. 


Hour. 


Temp- 
erature. 


Humid- 
ity. 


Evapo- 
ration. 


Lower 
surface 
coated. 


Uncoated. 


Upper 
surface 
coated. 


Aug. 6. . 


gh 45m p m 


62 


90 
















Aug. 7.. 


6 00 a.m. 
8 00 a.m. 


61 
62 


95 
95 


0.98 
.72 











0.20 
.39 


0.201 
.538 


0.08 


0.115 


0.26 


0.365 




10 00 a.m. 


66 


88 


1.44 


.30 


.208 


.60 


.417 


.61 


.426 




12 00 p.m. 






3.00 
2.49 


.83 
.35 


.278 
.140 


1.24 

.88 


.415 
.351 


1.33 
1.15 


.445 
.463 


2 00 p.m. 


63 


95 




4 00 p.m. 


62 


95 


2.56 


.38 


.147 


.70 


.276 


.91 


.355 




6 00 p.m. 


61 


92 


2.52 


.23 


.092 


.55 


.218 


.66 


.261 




9 00 p.m. 


61 


82 


4.04 


.48 


.118 


.56 


.139 


.76 


.18 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



87 



relative amounts of transpiring surface per unit volume in desert and 
rain-forest plants is, of course, profoundly concerned in the determina- 
tion of the absolute amounts of water lost by plant individuals. The 
prevalent conception that plant transpiration is reduced in desert plants 
arises from a consideration of the reduced transpiring surface of desert 
plants rather than from a knowledge of their water loss per unit area 
as compared with hygrophilous plants. 

Table 33. Influence on transpiration exerted by coating upper or lower leaf surfaces. 

Series run in laboratory, with three individuals of Diplazium celtidi folium, by weighing 
method. First group of readings on uncoated plants, second on plants coated as indicated. 
Leaf areas: (top and bottom): A, 222.6 sq. cm.; B, 227.1 sq. cm.; C, 181.9 sq. cm. 



Date. 


Hour. 


Evapora- 
tion. 


Uncoated. 


Diplazium A. 


Diplazium B. 


Diplazium C. 


T 


T 
E 


T 


T 
E 


T 


T 

E 


Nov. 18 

Nov. 19 


5 h 10 p.m. 
9 40 a.m. 
11 40 a.m. 
1 40 p.m. 
3 40 p.m. 














8.88 
13.86 
23.55 
20.91 


2.23 
4.23 
6.66 
6.45 


0.251 
.305 
.283 

.308 


2.44 
4.75 
7.48 

6.87 


0.275 
.343 
.317 
.328 














8 . 37 


0.400 




6 40 p.m. 


13.44 


3.52 


.262 


3 . 27 


.244 


4.96 


.369 


Nov. 20 


9 4C a.m. 


5.31 


1.58 


.298 


1.80 


.338 


2.49 


.469 




11 40 a.m. 


15.69 


5.36 


.342 


5.61 


.358 


6.93 


.441 




1 45 p.m. 


25.05 


7.21 


.288 


s L\y 


.330 


10.22 


.408 


Date. 


Hour. 


Evapora- 
tion. 


Lower surface 
coated. 


Uncoated. 


Upper 

coa 


surface 

ted. 


Nov. 20 


2 h 15 m p.m. 
5 25 p.m. 
















29.37 


3 . 37 


0.114 


8 . 5 1 


0.289 


8.37 


0.285 


Nov. 21 


8 15 a.m. 


12.57 


1.36 


.109 


3.57 


.289 


3.74 


.297 




11 15 a.m. 


15.39 


1.98 


.128 


5.91 


.386 


5.46 


.354 




4 15 a.m. 


12.18 


1.54 


.126 


4.36 


.358 


3.95 


.324 




7 15 a.m. 


10.74 


1.24 


.116 


3 . 1 2 


.290 


3.07 


.286 


Nov. 22 


9 45 a.m. 


8.64 


.92 


.106 


2.62 


303 


2.64 


.305 



RELATIVE AMOUNTS OF STOMATAL AND CUTICULAR 

TRANSPIRATION. 

The thinness of epidermal wall and lightness of cutinization which 
are well known to characterize rain-forest plants made it seem desirable 
to differentiate between stomatal and cuticular transpiration and to 
attempt an estimation of their comparative amounts. In the lack of a 
direct method of differentiating between the stomatal water loss and thai 
from the epidermis of both upper and lower leaf surfaces, the following 
indirect means of obtaining approximate values for them was employed. 

Three potted plants of the same species were run simultaneously in 
order to obtain a calibration of their rates of transpiration with respect 
to each other. After being run together through one day, the upper 



ss 



A MONTANE RAIN-FOREST. 



surfaces of the leaves of one plant were coated with molten cocoa butter, 
the under surfaces of the second were so coated, and the third was 
left uncoated as a control. In this condition the three plants were 
again run through one day. It was only after the completion of such 
a series, the determination of the leaf areas, and the calculation of 
the results that it was possible to know how evenly matched the rates 
of the three plants were before coating, and this made necessary such 
liberal discarding of results that only two such experiments were found 
to be as satisfactory as might be desired (see tables 22 and 33). 



-2.50 



2.00 



1.50 



1.00 



1.50 




A '. 



50 c / // 

/ / 

B f J 

A 



/ r /\ ; . v 

/;/\ / \: 
/ // \ / \\ 

\ X 




^ 



\/ 



' Tisn / / 



Unc ' / / 



i' i 

A 

// 

\ 



/ 

/ 
/ 



\ 



/ 



/ 



/ 



\/ 



sc/ 



i i r 



1 1 I 1 I 



fi a. m g io 12 2 ' m 4 



in 12 J P M 4 li 



Fig. 13. Normal daily march of transpiration for three plants of Pilea. 
and march for same plants on succeeding day after leaves of C had 
been coated on upper surface (USC), those of A had been coated on 
lower surface (LSC), and those of E had been left uncoated (Unc) 

as a control. Suspended curve is concurrent evaporation, plotted 

p 
to one-fourth of scale f - \ . 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



89 



It has long been known from the work of Comes 1 that the sum of 
the transpiration of the lower leaf surface alone and the upper surface 
alone is greater than the rate from a normal uncoated leaf. I am able 
to confirm this, as may be seen by comparison of D and E in table 34, 
indicating an average increase of 34 per cent in top alone plus bottom 
alone over the uncoated leaf, in Diplazium (see fig. 13). I have taken 
for granted that the amounts by which the transpiration of top alone 
and bottom alone are increased by coating the opposed surface are 
proportional to the normal rates themselves, an assumption which can 
not be far from the truth. On this assumption I have divided the 
amounts of transpiration in the uncoated plant, hour by hour, into 
two amounts, which are proportional to the amounts of water loss from 
the top alone and the bottom alone in the coated plants. This calcu- 
lation gives the approximate amounts of transpiration for the top and 
the bottom of an uncoated leaf (G in table 34), hour by hour. As the 
degree of cutinization is alike on the two sides of the leaves of the plants 
used, and as the epidermal walls are of almost the same thickness 
on the two sides, the cuticular transpiration of the bottom of the leaf, the 
stomata eliminated, is practically the same as that of the top of the leaf. 
The total area occupied by the stomata is so small as to be practically 
negligible. The actual stomatal transpiration is, therefore, the differ- 
ence between the calculated transpiration amounts for the upper and 
lower leaf surfaces (H, table 34). The values for true stomatal trans- 

Table 34. Showing method used to determine actual stomatal and cuticular transpiration. 
Diplazium celtidifolium. (Based on data given in table 33.) 



5 h 25 n 
p.m. 



8 h 15 m 


ll h 15 m 


p.m. 


p.m. 


1.36 


1.9S 


3.74 


5.46 


36.40 


36.20 


5.10 


7.44 


3.57 


5.91 


42.70 


25.80 


.95 


1.57 


2.62 


4.34 


1.67 


2.77 


46.70 


46.80 


1.90 


3.14 


.132 


.179 


.152 


.'_'!> 1 



4 h 15 m 
p.m. 



7 h 15 ra 
p.m. 



Qh 45m 

p.m. 



B. 



D 
E. 
F. 

G. 



H. 

I. 

J. 
K. 

L. 



Transpiration of upper surface with 

lower coated 3 . 37 

Transpiration of lower surface with 

upper coated 8 . 37 

Percentages of A to B (average 37. SO 

per cent) 40 . 20 

The sum of A and B 11 .74 

Transpiration of uncoated leaves 8.51 

Percentage of increase of D over E 

(average 34.30 per cent) 38 . 00 

E divided into amounts proportional 
to A and B: calculated transpiration 
upper and lower surfaces in un- 
coated leaves: 

Upper surfaces 2.44 

Lower surfaces 6 . 07 

G-LminusG-U: stomatal transpiration 3.63 
Percentage of H to E (average 45.10 

per cent) 42.70 

E minus H: cuticular transpiration. . . 4.88 
Ratio of H to evaporation: relative 

stomatal transpiration I . l-'^i 

Ratio of J to evaporation: relative 

cuticular transpiration | . 166 



1.54 

3.95 

38.90 
5.49 
4.36 

25.60 



1 _'_' 
3.14 
1.92 

44.00 

_' II 

.157 
.200 



1.24 
3.07 



0.92 
2.64 



40.60 34.70 

4.31 , 3.56 

3.12 ; 2 62 

38 20 35.70 



.90 

2 _ _ 

1 32 



12 30 

1 M) 



,123 
168 



68 
1 94 
l 26 

is 10 
1 36 

.147 

.156 



'Comes, O. Azione della temperature, della umidita relativa et della Luce sulla transpiratione 

delle piante. Rendic. d. R. Acad. d. Science di N'apoli. 1S7S. 



90 



A MONTANE RAIN-FOREST. 



piration (as distinguished from the transpiration of the lower surface) 
air found to be from 42 to 4S per rent of the total transpiration of the 
leaf. In other words, in Diplazium the total epidermal surface of the 
leaf Loses at all times slightly more water than the stomata. 

The relative stomata! and the relative cuticular transpiration have 
been calculated from these readings (table 34, K, L). A comparison 
of these two sets of relative transpiration figures shows that the fluctua- 
tions in the diurnal march of the relative cuticular rate are only slightly 
less than the fluctuations of the relative stomatal rate (see fig. 14). 
This evidence indicates that the irregularities of relative transpiration 
rate are due to some physiological regulations other than the opening 



200 


CT / ... \^ 

ST ' 

E 


- 


-.100 








e\ 






2 \ 




12 


\ 


- 


10 


t \ 


- 


-8 


\\ y\ 




6 


A/\\ 


- 


-4 


st.. \ \/ \. 




2 




- 


5.25 p| 8.15A-M hi:. J.ir.i'' 7,15 |<u.",am 



Fig. 14. Curves of stomatal transpiration (ST), cuticular transpiration 

.p. 
(CT), total transpiration (T), and evaporation ( ) lor Diplazium, 

ST 
together with the rates of relative stomatal transpiration ( -") and 

CT ^ 

relative cuticular transpiration ( -^r) . 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 91 

and closing of stomata in other words that the principal regulatory 
functions reside within the leaf itself and are perhaps active, perhaps 
passive agents in determining the rate of water loss through the 
stomata, whatever may be the state of their openness. 

The evidence of the curves of relative stomatal and cuticular trans- 
piration depends for its value on the normal stomatal behavior of the 
plant in which the upper surfaces of the leaves were coated, a matter 
which could not be investigated during the transpiration weighings, 
by any available method. 

Pilea nigrescens was used in the second experiment, the detailed 
results of which are not given. In this test the average increase of 
top alone plus bottom alone over the uncoated leaf was 77 per cent, 
and the average percentage of the actual stomatal transpiration to the 
total transpiration of the uncoated leaf was 41 per cent. The latter 
percentage indicates that the ratio between the stomatal transpiration 
and the actual total cuticular transpiration is of the same order of 
magnitude in Pilea and in Diplazium. The matter of the number of 
stomata per unit area, which I have not determined, is an important 
factor in affecting this ratio, as also is the amount of cutinization and 
thickening of the epidermis. 

STOMATAL BEHAVIOR. 

The possession of relative transpiration data greatly clarifies the 
investigation of the influence of fluctuations of stomatal movement on 
transpiration. The effects of wind, temperature, and humidity are 
eliminated by their use, and it is possible to compare stomatal condition 
with the fluctuations of transpiration which are due to internal factors. 
Such internal factors, whether active or passive in their agency, are 
alone responsible for the departures of the relative transpiration curve 
from a straight line parallel to the axis of abscissas. 

My purpose in securing readings of stomatal aperture concurrently 
with transpiration weighings was to learn in how far the changes of 
stomatal openness might be correlated with the fluctuations of relative 
transpiration rate. The existence of a positive 1 correlation might be taken 
as proof of the control of relative transpiration by stomatal movement . 
or as proof that stomatal movement and the fluctuations of the relative 
transpiration are both governed by more deep-seated internal factors. 

The methods by which I measured transpiration and secured stomatal 
readings were such that I necessarily obtained my epidermis for the 
latter purpose from other individuals than those in which the transpira- 
tion was being measured. This is an extremely unfortunate limitation 
to the combined use of the weighing method oi determining trans- 
piration and Lloyd's method for stomatal measurement. I secured 
epidermis from potted plants which had had the same history as those 
that were being weighed, which looked just like them in general char- 



92 



A MONTANE RAIN-FOREST. 



actor of foliage, and were placed alongside them during the intervals 
between weighings. I am unable to say in how far the results which I 
am about to give have been modified by the limitations of the methods 
used. The fact, however, that all of the evidence which I have secured 
for four species of plants fails to show any serious discordance leads 
me to believe that the plants used for transpiration and those used 
for stomata did not behave in such a dissimilar manner as to destroy 
the validity of my conclusions. 

In making measurements of stomatal aperture from the stained and 
mounted pieces of epidermis, by means of a micrometer eye-piece, I 
commonly took readings from 24 stomata in each preparation. Unlike 
other workers who have used this method I did not discard the extreme 
readings, nor fail to measure the most divergent stomata observed, but 
measured all stomata throughout a path across the piece of epidermis. 

A considerable degree of variability w r as disclosed in the openness 
of the stomata in nearly all of the preparations of epidermis. The 
variability of diameter in two plants, Peperomia turfosa and Diplazium 
celtidifolium, is indicated by the data in table 35. Peperomia exhibits 
its widest variability at the first two morning readings, and shows 
considerable constancy at noon, again becoming variable in the after- 
noon. Diplazium shows a less range of variability, as well as a more 
constant diameter throughout the day. These are given as typical 
cases of stomatal variability and they have been treated, as have all 
other sets of readings, as the normal behavior of the plants concerned, 

Table 35. Variability of stomatal diameter in Peperomia turfosa and Diplazium celtidifolium, 

October 16, 1909. 



The 


number of stomata read in diameter groups of 10 microns. Heavy figures 
indicate the group in which the maximum number of stomata fall. 


Peperomia turfosa. 


Hour. 





0-10 


10-20 


20-30 


30-40 


40-50 


50-60 


60-70 


70-80 


80-90 


90-100 


100-110 


110-120 


6 a.m. 

8 
10 
12 

2 p.m. 


4 


1 
2 


10 

5 

2 


7 
1 

1 
1 


4 
G 


1 
3 

6 


1 
4 
7 
9 
2 


1 

4 

5 

10 

1 


2 
2 

8 
8 
2 


1 

1 
1 






































1 
4 
5 
1 


8 

1 


3 


1 




4 
6 
9 






6 
7 

2 


1 
4 


3 
5 
1 


10 


2 

14 


7 
9 




2 
































Diplazium celtidifolium. 




















3 
2 
3 
1 
7 
7 
4 
4 


7 

4 

5 

11 

6 
2 
2 

2 


7 
3 
7 
6 
3 
6 


1 




8 
10 
12 

2 p.m. 














1 
3 


1 
4 
1 
6 
3 
3 
3 














1 

3 


1 


























2 

1 

11 

7 


4 
6 
9 














5 












1 
2 


3 

1 










1 



















TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



93 



and the averages of the variable readings have been used in the tables 
and curves. As already stated, the measurement of twice the usual 
number of stomata gave, in no case, a greater difference than 6 per 
cent between the average diameter of the two groups of 24. 

In table 36 and fig. 15 are given the curves for two experiments with 
Peperomia iurfosa in which the stomatal readings were taken. The 
first of these was interrupted at 2 p. m., up to which hour there had 
been a nearly constant rise of the curves of transpiration and relative 
transpiration, and a general upward course in the evaporation after 
8 a. m. The curve of stomatal openness rises in good agreement with 
the relative transpiration curve, but reaches a maximum at 12 noon 
and falls at 2 p. m., in spite of the rise in relative transpiration during 
the same interval. 




Fig. l."). -Graphs f"r two experiments with Peperomia turfosa in 

which determination was made of transpiration (T), evapora- 
tion ( ), relative transpiration (=), and stomatal area B 



94 



A MONTANE RAIN-FOREST. 



In the second experiment there is a sharp break in the morning rise 
of the evaporation curve, accompanied by a lessening in the rate of 
increase of transpiration. These checks are accompanied by a fall in the 
relative transpiration, which then continues to rise throughout the re- 
mainder of the day. The fall in relative transpiration at noon is accepted 
by a fall in stomatal openness, giving the curves of relative transpi- 
ration and stomatal movement 
a good agreement for the day. 

In an experiment with Pilea 
nigrescens (table 37, fig. 16) 
which was performed along 
with the first one on Peperomia 
turfosa, already described, and 
was discontinued at 2 p. m., w f e 
have a gradual rise in stomatal 
openness until 2 p. m., together 
with a rise in the relative tran- 
spiration up to 12 noon, and a 
slight fall thereafter. The shape 
of the curves of rise for the two 
are unlike, and between 12 and 
2 p. m. there is the slight fall of 
relative rate in spite of a con- 
tinued increase of the stomata. 
The increase of stomatal open- 
ness between 12 and 2 p. m. was 
greater, in fact, than that be- 
tween 8 and 10 a. m., but in 
the latter case there w r as a 
sharp rise in the relative rate, accompanying a rapid rise of evapora- 
tion. The 6 a. m. readings of evaporation and transpiration in this 

Table 36. Transpiration, relative transpiration, and stomatal behavior in Peperomia turfosa. 

Series run in laboratory; transpiration by weighing method; stomata from potted 
plants under same conditions as those weighed. 



wdZ 81 [ vy 




/^"^I 




/ 




/ /I 

/ 




-*4d \ 




/ ^ 





Fig. 16. Graphs for evaporation ( :). and for 
transpiration (T), relative transpiration (p), 



E 



and stomatal area (S) of Pilca nigrescens. 



Date. 


Hour. 


Evapora- 
tion. 


T 


T 
E 


Stomatal 
width. 


Stomatal 
length. 




VwXl 


Julv 30 
July 31 

Aug. 17 

Aug. 18. . . . 


6 p.m. 

6 a.m. 

8 
10 
12 p.m. 

2 

9 p.m. 

8 a.m. 
10 
12 p.m. 

2 

4 

6 


6.96 
3.24 
6.48 
6.30 
7.44 

2.64 
9.00 
10.92 
12.42 
8.94 
6.18 


0.31 
.23 

.74 
.74 

.97 

.12 
1.44 
1.56 
2.50 
2.26 
2.03 


0.044 
.069 
.114 
.118 
.131 

.044 
.155 
.143 
.202 
.254 
.337 


2.4m 

3.6 

5.1 

6.2 

5.4 

3.5 

4.5 
4.1 
4.6 
5.4 


16.1m 

19.9 

22.9 

24.2 

24.9 

17.2 
18.2 
13.8 
16.9 
17.7 


6.22 

8.47 

10.80 

12.25 

11.55 

7.76 
9.04 
7.52 

8.82 
9.78 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



95 



experiment are from over-night readings, and are not to be correlated 
with the stomatal conditions at 6 a. m. 

On October 16 simultaneous determinations of stomatal openness 
were made on Peperomia turfosa, Pilea nigrescens, Diplazium celtidi- 
folium, and Asplenium alatum, in connection with transpiration and 
evaporation readings (table 38, figs. 17 and 18). Peperomia turfosa 



Table 37. Transpiration, relative transpiration, and stomatal behavior in Pilea nigrescens. 

Series run in laboratory; transpiration by weighing method; stomata from 

accompanying potted plants. 



Date. 


Hour. 


Evapora- 
tion. 


T 


T 

E 


Stomatal 
width. 


Stomatal 
length. 




VwXl 


July 30 
July 31 


6 p.m. 

6 a.m. 

8 
10 
12 p.m. 

2 


6.96 
3.24 
6.48 
6.30 
7.44 


0.43 
.38 
.89 
.93 

1.10 


0.062 
.116 
.138 
.149 
.148 


2.2 
2.5 
2.5 
3.8 
4.5 


10.3 
10.2 
10.8 
12.9 
12.9 


4.76 
5.10 
5.20 
7.00 
7.62 



Table 38. Transpiration, relative transpiration, and stomatal behavior in five species investigated 

simultaneously. 



Series 


run in laboratory; 


transpiration bj 


r weighing method; stomata frorr 


accompanying potted plants. 


Date. 


Hour. 


Evapo- 
ration. 


Peperomia turfosa. 


Pilea nigrescens. 


T 


T 

E 


Stoma- 
tal 


Stoma- 
tal 




T 


T 
E 


Stoma- 
tal 


Stoma- 
tal 




VwXl 


VwXl 










width. 


length. 






width. 


length. 




Oct. 16 


6 a.m. 


6.36 


0.21 


0.03:! 


3.1 


21.0 


8.08 


0.23 


0.036 


3.2 


11.6 


6.09 




8 


4.50 


.13 


.028 


3.8 


17.2 


8.09 


.19 


.041 


3.1 


11.3 


5.92 




10 


11.77 


.77 


.066 


4.8 


20.5 


9.92 


.79 


.067 


3.4 


12.6 


6.53 




12 p.m. 


23.01 


1.48 


.064 


6.5 


23.0 


12.23 


1 . 58 


,068 


4 . 5 


16.7 


8 67 




2 


1 6 . 20 


.78 


.049 


7.9 


19.8 


12.51 


1.05 


.064 


5.6 


14.5 


9.01 




4 


13.95 


.39 


.028 


4.4 


19.4 


9.24 


.73 


.052 


.8 


16.0 


3.62 




6 


16.72 


.37 


. 022 


2.5 


17.9 


6.68 


.33 


.020 


2.3 


11.8 


3 58 




9 


7.80 


.10 


.013 


.0 


20.7 


3.52 


.19 


.024 


2.2 


12.6 


5. IT, 


Date. 


Hour. 


Evapo- 
ration. 




Diplaz 


urn celtidifoliun 


. 




Asplenium a 


latum. 




V 


T 

E 


Stoma- 
tal 


Stoma- 
tal 




T 


T 

1. 


Stoma- 
tal 


Stoma- 
tal 




VwXl 


VwXl 










width. 


length. 






width. 


length. 




Oct. 16 


6 a.m. 


6.36 


0.70 


0.111 


8.3 


22 i 


L3.54 


1.02 


0.160 


l 6 


15 7 


8 in 




8 


4.50 


.42 


.094 


8 2 


L9.5 


12.64 


66 


.117 


l 9 


16.0 


B 36 




10 


11.77 


1.17 


.099 


8. 1 


18. ) 


12.21 


l 13 


122 




15 ii 


8 83 




12 p.m. 

9 


23 01 


2 32 


100 


8 9 


mi 2 


13 37 


2 Jl 


1 1 16 










16.20 


1.60 


.098 


7.6 


18 5 


1 1 85 


1 92 


.118 


:, (i 


l l 2 


8. 13 




4 


13.95 


1. 01 


.072 


8 ii 


20.6 


12 85 


I 30 


.093 


l 7 


19 9 


g 68 




6 


16.72 


.93 


.055 


6 ii 


21 ii 


1 l . 22 


111 


(His 


2.4 


12.8 


:, :,i 




9 


7.80 


.64 


.082 


6. t 


2] 2 


11 .65 


1 36 


111 


3 '.i 


16.9 


8.12 



in; 



A MONTANE RAIN-FOREST 



Bhows a niaxiimim of the daily relative transpiration at 10 a. in., the 
maximum f or evaporation and transpiration at 12 noon, and the maxi- 
mum of stomatal aperture at 2 p. m. Between 10 and 12 a. m. there 
was a pronounced increase in the stomatal openness, which was accom- 




Fig. 17. Curves for simultaneous experiments with Peperomia turfosa (upper) and Pilea nigres- 
cens (lower) which determination was made of transpiration (T), relative transpiration 



( ), stomatal area (S),and evaporation ( 



E 



-J- 

10' 



panied by a plateau in the curve of relative transpiration. Between 
12 and 2 p. m. there was a considerable fall in the relative rate at the 
same time that the stomatal aperture was still increasing. The curves 
for Pilea show a general similarity to those for Peperomia : there is the 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



97 



daily maximum of transpiration and evaporation at 12 noon, with a 
plateau in the curve of relative transpiration between 10 a. m. and 
2 p. m., accompanied by a sharp rise in the curve of stomatal openness 
between 10 a. m. and 12 noon, and a less rise between 12 and 2 p. m. 




1 

E 




Fig. 18. Curves for simultaneous experiments with Diplazium celtidifolium (upper) 
and Asplenium alatum (lower). These experiments were carried out on the same 
day as those with Pcperomia and Pilea (fig. 17). The curves are: transpiration (T), 
evaporation (.,). relative transpiration (.-,), and stomatal ana (S). 



In the afternoon, between 4 and 6 o'clock, then 1 is a rapid fall in the 
relative rate, with no accompanying change in the stomatal openness; 
between 6 and 9 p. m., however, the two rise in company. 

The daily march of stomatal openness for Diplazium is extremely 
uniform. The transpiration of the plant followed the evaporation 



'.IS a MONTANE RAIN-FOREST. 

with remarkable exactness from 6 a. m. until 2 p. m., after which hour- 
it continued to fall during the occurrence of a secondary maximum of 
evaporation, culminating at 6 p. m. There is as much disagreement 

as there is agreement in the curves of relative transpiration and stoniata 
movement from (i a. m. to 4 p. m. The close parallelism of the trans- 
piration and evaporation curves is very striking as compared with the 
divergent behavior of the relative transpiration and stomatal curves 
and points to the impotence of stomatal movements in counteracting 
the influence of evaporation rate on transpiration, at least during the 
mid-day hours. From 4 p. m. until 9 p. m. the curve of transpiration 
lay below that of evaporation (plotted as one-tenth of the actual 
readings), and during these hours there is a certain degree of correlation 
between the relative transpiration and stomatal behavior: they fall 
together from 4 to p. m., but the rise in the relative rate between 6 
and 9 p. m. is too great to be accounted for by the slight rise in stomata 
openness. 

The series of stomatal readings for Asplenium is unfortunately marred 
by the loss of the 12 noon datum. Even in its absence, however, it 
is possible to observe the fall of relative rate between 8 and 10 a. m., 
accompanied by a constant stomatal openness, and the pronounced 
fall of relative rate between 2 and 4 p. m., during an increase in stomatal 
aperture. Here again, as in the case of Diplazium, there is a close 
parallel between the rates of transpiration and evaporation until 4 p. m. 
after which hour there is a parallelism between relative transpiration 
and stomatal behavior that is entirely lacking through the earlier part 
of the day. The opening up of the stomata between 6 and 9 p. m. in 
Diplazium is still more pronounced in Asplenium, where the transpira- 
tion rises with it. This occurs in both plants in spite of a sharply 
falling rate of evaporation, and this also occurred at the same time in 
Pilea nigrescens (fig. 17). 

If a correlation of relative transpiration and stomatal movement is 
to be interpreted as proving that the latter controls the former, the 
total evidence which I have secured indicates that stomatal move- 
ments are of minor importance in regulation of transpiration. The 
lack of a constant correlation between the relative transpiration behavior 
and stomatal movement bears also on the question of the regulation 
of stomatal openness by the water-content and other conditions of the 
leaf, a problem on which I have no data. 

My experiments show, in general, that there is a lack of correlation 
between the relative transpiration and stomatal movements during the 
mid-day, and that in the late afternoon and early night there is a 
positive correlation. This means that the evaporating power of the 
air and the water-losing capacity of the plant stand in such a close 
correlation during mid-day that the degree of stomatal aperture is 
incapable of exerting a positive controlling influence. Under the lower 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



99 



evaporation of the late afternoon and early night, and in the absence 
of light which is always to be reckoned with in its immediate effects 
on transpiration the conditions of stomatal openness are capable 
of an apparent regulation of relative transpiration. 



Table 39. Influence of darkness on transpiration. 

Amounts of transpiration and relative transpiration for Pilea nigrescent and Peperomia tnrfosa 
in the diffuse light of the laboratory and in a dark chamber. Humidity was determined 
by psychrometer and by polymeter. 



Date. 



Sept. 17 
Sept. 18 



Sept. 19. 
Sept. 20. 



Hour. 



Tem- 
pera- 
ture 



6"' 
9 
11 
1 
3 
6 



00" 

30 

30 

30 

30 

30 



p.m. 
a.m. 
a.m. 
p.m. 
p.m. 
p.m. 



66 
69 
75 
69 
69 
67 



9 30 a.m. 

7 30 p.m. 

8 40 a.m. 
6 30 p.m. 



67 
66 
60 
66 



Humidity. 



Psy. 



95 
91 
87 
91 
89 
93 



Pol. 



98 
94 
86 
93 
90 
97 



Pilea 
Evap- \ nigreseens, A. 
ora- 
tion. T 
E 



1.26 
10.12 
15.30 

8.77 
10.10 



0.10 

1.08 

1.08 

.67 

.64 



97 
98 
98 
97 



3.90 
3.38 
3.62 
2.44 



.23 

.28 
.19 
.20 



. 0*0 
.107 
.070 
.071 
.063 



Pilea 
nigreseens, B. 



Peperomia 

turfosa. 



T 
E 



0.16 0.124 



1.35 ' 

1.49 I 

.86 I 

ss 



.133 

.097 
.098 
.087 



.061 

.052 

.083 



. 30 . 07S 

.37 .111) 

.26 .074 

::i .130 



(i n> 
.88 
.62 
.31 
.38 



.07 
.13 
.09 
.07 



E 



0.067 

(ls7 

.040 

.036 

.037 



(117 
.038 

.024 
.030 



Averages in light: 

1 nocturnal reading. 
4 diurnal readings. . . 

Averages in darkness: 

2 nocturnal readings. 
2 diurnal readings. . . 



0.080 




0.124 




.078 




.104 




.056 




.076 




.084 




.120 





0.067 
.050 

.021 
.034 



INFLUENCE OF DARKNESS ON TRANSPIRATION. 

The securing of relative transpiration rates is of great value in the 
investigation of the influence of individual factors on the rate of 
transpiration. It is impossible, for example, to determine the rate of 
transpiration of a plant in the light and then to place it in darkness 
without changing other factors than the light. Such changes, notably 
in air movement and humidity, are of strong influence upon the rati' 
of absolute transpiration, but without influence on the relative rate. 
I was interested in the influence of darkness on transpiration in con- 
nection with the general question of stomatal behavior and in connec- 
tion with the relation between the diurnal and nocturnal transpiration 
activities of rain-forest plants. With the means at hand to secure 
relative transpiration rates. I made two tests of the rate for plants 
placed first in the diffuse light of the physiological laboratory, and 
afterwards in the dark chamber which has been described. 



100 



\ m )\ I A.NE RAIN-FOREST. 



The first test (table 39) involved two plants of Pilea nigrescens and 
one of P< />< ram la (urfosa. The series was run over night and through 
one day in the light, and was then placed in darkness for 48 hours, 
readings being taken each morning and evening. On comparing the 
rates of relative transpiration for the first night and the averaged rates 
for the day in the light, the latter will be found to be the lower of the 
two. The rates for the first night were, however, considerably higher 
than those for the two nights in the dark chamber. The averaged 
rates for the day in the light are lower than the diurnal readings in the 
dark chamber in the case of Pilea, but are higher in Peperomia. The 
rates for the first and second days and for the first and second nights 
in the dark chamber are in fairly close agreement. The evidence of 
the two plants of Pilea is in agreement in showing an increase in 
relative rate due to darkness, while Peperomia shows a decrease in rate. 

Table 40. Influence of darkness on transpiration. 





Amounts of transpiration and relative transpiration for five species, in 
of the laboratory and in a dark chamber. 


the diffuse light 




Date. 


Hour. 


Tem- 
pera- 
ture. 


Hu- 
mid- 
ity. 


Evapo- 
ration. 


Pilea 
nigrescens. 


Peperomia 
turfosa. 


Peperomia Diplazium 
basellsefolia. celtidifolium. 


Asplenium 

alatum. 


T 


T 
E 


T 


T 
E 


T 


T 
E 


T 


T 

E 


T 


T 
E 


Oct. 11 

Oct. 14 
Oct. 15 


7 b 00 m a.m. 
9 00 a.m. 
11 00 a.m. 
1 00 p.m. 
3 00 p.m. 
5 00 p.m. 
7 00 p.m. 
9 00 p.m. 

3 30 p.m. 
9 30 a.m. 
3 30 p.m. 


63 
70 
73 
72 
69 
67 
64 
63 


92 

89 
83 
83 
89 
90 
93 
92 
























3.07 
12.00 
16.12 
15.52 
11.02 
5.85 
4.27 


0.34 
.75 
1.09 
1.03 
.57 
.26 
.19 


0.111 
.051 
.067 
.066 
.051 
.044 
.045 


0.21 
.76 
.92 
.87 
.50 
.15 
.31 


0.068 
.063 
.057 
.056 
.046 
.026 
.074 


0.18 
.57 
.66 
.48 
.25 
.20 
.17 


0.058 
.048 
.041 
.031 
.023 
.035 
.039 


0.52 

1.12 

1.43 

1.25 

.87 

.44 

.41 


0.169 
.093 
.089 
.080 
.079 
.076 
.097 


0.84 
1.55 
1.80 
1.56 
1.23 
.64 
.63 


0.274 
.129 
.112 
.100 
.112 
.109 
.147 





74 
85 
85 






















7.61 
6.07 


.31 
.55 


.041 
.090 


.20 
.29 


.027 
.048 


.23 
.34 


.030 
.056 


1.23 
1.20 


.096 I 1.06 
.115 1.12 


.139 
.185 


Average of 7 readings in li 


ght 


0.062 
.065 




0.056 
.038 




0.039 
.043 




0.098 
.106 


. . 


0.140 
.162 


arkness 













The second experimental series (table 40) involved the five species 
which have heretofore been mentioned: Pilea nigrescens, Peperomia 
turfosa, Peperomia basellcefolia, Diplazium celtidifolium, and Asplenium 
alatum. These plants were run in diffuse light on October 11, and three 
days later were run in the dark chamber from mid-afternoon until 
mid-morning of the following day, and again to mid-afternoon of the 
second day. The time of taking these readings is such that nocturnal 
and diurnal rates in the darkness can not be compared. A comparison 
of the averaged rates for the seven readings in the light with the single 
diurnal rate in the darkness shows that the darkness rate was higher 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 101 

for all of the species excepting Peperomia turfosa. A comparison of 
the averaged rates in the light with the average of the two sets of 
darkness readings, nocturnal and diurnal, brings out the same behavior, 
in which Peperomia turfosa is the only form showing a lowering of rate 
due to darkness. 

In each of the experiments and in each plant investigated there was 
a maximum of relative transpiration in the light which was well in 
excess of the darkness rate. Rates which approach the daily maximum 
in amount are, however, of infrequent occurrence in series of two-hour 
readings, with the result that daily averages are low as compared with 
the maximum rates. 

The influence of darkness on the aperture of stomata was briefly 
investigated in Pilea nigrescens and Peperomia turfosa. Plants of these 
species were placed in a dark chamber for three days, and at the end 
of the period material for stomatal examination was taken in the usual 
manner, without exposing the plants to any more light than was 
necessary for the operation. The resulting measurements give for 
Pilea: width 5.24^, length 14.01 M ; Peperomia: width 5.39^, length 
20.17^. The values for VlXw are respectively: 8.53 and 10.43. For 
plants in the light, the figures given for stomatal aperture in Pilea 
(table 37 and 38) show daily maxima of 7.62 and 9.01, readings with 
the average of which the darkness aperture of 8.53 is in near agreement. 
The daily maxima in the light, as determined for Peperomia (tables 36 
and 38) are 12.25, 9.78, and 9.01, amounts which are also of the same 
order of magnitude as the darkness determination of 10.43. 

Lloyd states 1 that in plants of Verbena ciliata placed in prolonged 
darkness the stomata perform the usual nocturnal closure and remain 
closed. Several earlier workers, using various and usually unreliable 
methods, have stated that there is an opening of stomata in prolonged 
darkness, usually following a closure during the first few hours. 

While I can not maintain from single readings on two plants that 
the stomata are constantly as wide open in darkness as the above 
figures indicate, nevertheless the probability is extremely strong that 
none of the possible fluctuations of aperture in darkness carry the 
stomata to a degree of openness much below the possible normal daily 
maximum under light conditions. It will be seen from the data in 
table 28 that Pilea and Asplenium show a sharp increase of stomatal 
area between 6 and 9 p. m., while Diplazium shows a Blight increase- 
behavior which is in accordance with the readings taken in darkness 
and is indicative of a possible failure of the stomata to close on first 
being placed in darkness. No other results were secured which throw 
light on this matter. 

The fact that the stomata of plants placed in prolonged darkness 
show a degree of openness similar to the somewhat transitory daily 

^loyd, F. E. The Physiology of Stomata. p. 115. Carnegie [net. Wash. Pub. ^-', 1908 



102 



A MONTANE RA1N-FOHKST. 



maximum of plants in light, and that such a degree of openness is 
probably maintained throughout the 24 hours, is in accordance with 
the high rales of relative transpiration already stated as occurring in 
plants placed in darkness. Livingston has reported 1 a higher rate of 

relative transpiration by night than by day for certain species of cacti, 
a phenomenon in which stomatal behavior is probably not concerned. 
Although stomatal behavior has been shown in a preceding section n<>l 
to be the controlling factor in the diurnal fluctuations of transpiration 
in the rain-forest plants which I have investigated, it does show r an 
increasing tendency toward such control in the later hours of the day, 
and the results just given indicate that the wide openness of stomata 
in prolonged darkness is responsible for the high rates of relative trans- 
piration in darkness, I have no evidence calculated to explain the 
aberrant behavior of Peperomia turfosa, in which the relative rate is 
lowered in the darkness. 

INFLUENCE OF HIGH HUMIDITY ON TRANSPIRATION. 

The retarding influence of high percentages of humidity on the rate 
of absolute transpiration is well knowm both upon experimental and 
theoretical grounds. I have taken the opportunity to investigate the 
rates of absolute and relative transpiration under conditions of high 
humidity in the five species already mentioned as used in other experi- 
mental work. The plants were placed in the moist chamber which 
has been described, and the humidity was kept above 90 per cent and 
usually above 95 per cent, the percentage being determined by means 
of a Lambrecht polymeter, calibrated for high humidities bj^ use of a 
sling psychrometer. The results as respects absolute transpiration are 
what was expected there is a decided cutting down of the rate. The 



Table 41. Transpiration of P 'ilea and Peperomia at high Itumidities. 
Scries run in moist chamber in diffuse light of laboratory. 



Date. 



Hour. 



Sept. 8. 
Sept. 9. 



2 p.m. 

10 p.m . 

6 a.m . 

2 p.m . 
10 p.m. 



Tempera- 
ture. 



75 
02 
59 
73 
59 



Humidity. 



Evapora- 
tion. 



Peperomia 
turfosa. 



Pilea 
nigrescens. 



95 
98 
98 
95 

98 



3.30 

1.33 

.67 

2.98 



0.16 
.04 
.09 
.11 



T 
E 






0.048 
.031 
.144 
.038 



0.31 
.12 
.25 
.37 



T 
E 



0.095 
.093 
.380 
.125 



Nocturnal reading . 031 

Average of 3 diurnal readings . 077 



. 093 
.200 



Livingston, B. E. Relative Transpiration in Cacti. Plant World, 10: 110-114, 1907. 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 103 

rates of relative transpiration, however, are not sharply reduced; in 
fact they are either of the same order of magnitude as in other experi- 
ments already commented on, or are even greater than in them (com- 
pare tables 41, 42, and 43, showing rates at high humidities, with tables 
23, 24, and 25). This is equivalent to saying that the degree to which 
the conditions of high humidity cut down water loss from the plant is 
equalled or exceeded by the rate at which they reduce the water loss 
of the atmometer. I have already called attention to the correcting 

Table 42. Transpiration of Pilea and Peperomia at high humidities. 
Series run in moist chamber. 













Pilea 


Pilea 


Peperomia 












oigrescens, A. 


oigrescens, B. 


turfosa. 


Date. 


Hour. 


Tem- 
perature. 


Humid- 
ity. 


Evapo- 
ration. 










T 




T 




T 












T 


E 


T 


E 


T 


E 


Sept. 20 
Sept. 21 


6 h 30 m p.m. 
9 00 a.m. 


66 


97 














66 


98 


0.73 


0.03 


0.039 


0.02 0.027 


0.01 0.011 




6 00 p.m. 


65 


98 


1.58 


.17 


.109 


.30 


.195 


.20 .129 


Sept. 22 


9 00 a.m. 


65 


98 


1.07 


.06 


.053 


.06 


057 


.12 i .111 




5 00 p.m. 


64 


98 


1.18 


.26 


.110 


.31 


.131 


.16 .067 


Sept. 23 


10 00 a.m. 


67 


98 


.21 


.01 


.025 


.06 


.145 


.01 .n.'s 




5 45 p.m. 


65 


98 


1.15 


. 26 


.115 


.52 


.L'-7 


.25 .109 

1 


Average of 3 nocturnal reading 












. 07(i 


051 








.111 


184 


102 























Table 43. Transpiration of five species nl lii<jh humidities. 
S< lies run in moist chamber. 



Date. 



Oct. 

11 



Hour. 



9 h 30 a.m. 

11 30 a.m. 

l :;n p.m. 

:>, 30 p.m. 



Aver- 
age 
tem- 
per- 
ature. 



Aver- 
age 
hum- 
idity. 



72.9 93.9+ 
79.8 98.0 

::, i '.2.4 



Evapo- 
ration. 



Pilea Peperomia 

hiurescens. turfosa 



.Mi,?, 
2.55 
6.30 



0.46 

58 

.01 



T 
E 



T 
E 



0.36 
1.228 .7(ni _'77 
.097 .35 .056 



Pepen imia Oiplazium 



basell SB- 
folia. 



ii 20 
.37 
. 29 



T 
E 



1 l' 
04< 



celtidi- 

folium. 



Ajsplenium 
alatum. 



T 
E 



,. T 

1. 



.51 0.74... 

7_'o 2851. OIK) 396 
..-.'.i .093 To . 1 1 * 



factor which must be introduced in comparing atmometric readings 
taken in climates of distinctly unlike conditionsof at mospheric humidity. 
The differences in the character of the water films presented by the 
atmometer under arid and under humid conditions would not be mani- 
fested between atmospheric conditions as similar as those in my moist 
chamber and those normally prevailing in the physiological laboratory 
at Cinchona, or would, at least, be so -mall as to be negligible. 



10 1 A MONTAM KAIN-FOREST. 

The rates of absolute transpiration obtained under moist-chamber 
conditions are of importance in the general correlation of my experi- 
mental work at Cinchona with my instrumentation within the rain- 
foresi proper. I have already alluded to the difference between the 
humidity and cloud conditions on the windward and leeward slopes of 
the Blue Mountains. My moist chamber experiments wen; performed 
under conditions more nearly like those of the Windward Ravines and 
Windward Slopes; the other laboratory experiments, however, were 
carried on under the normal shade conditions of the Leeward Slopes, 
on which the laboratory is situated. The low rates of absolute trans- 
piration secured in the moist chamber may be taken as closely parallel- 
ing the rates in the still air of Windward Ravines and in Windward 
Slopes throughout the greater part of all normal days. In spite of the 
approximate equality of the relative transpiration rates secured in the 
moist chamber and those secured in the open laboratory, the fact remains 
that the evaporation rate of the moist chamber and of the moist habi- 
tats of the rain-forest is extremely low, and the equality of the relative 
rates merely indicates that the transpiration is correspondingly low in 
the latter situations. 

Table 44. Coefficients of transpiration for open laboratory and for moist chamber. 





Laboratory. 


Moist 
chamber. 


Pilea nigrescens (Windward Slope) 


1.64 
1.54 
1.00 
3.38 
3.57 


1.79 
1.58 

1.00 
1.98 

2.58 


Peperomia turfosa (Windward Slope) 


Peperomia basellaefolia (Ridge) 

Diplazium celtidifolium (Windward Ravine) 





The plants of the Windward Ravines which were brought for experi- 
mentation into the somewhat drier atmospheric conditions of the labora- 
tory at Cinchona were subjected thereby to more active water loss. 
The plants of the Windward Slopes and Ridges which were brought 
into the laboratory were not subjected to so great a change from the 
conditions prevailing in their natural habitats. By reason of this 
circumstance it is instructive to compare the rates of transpiration of 
the several species inter se under each of the two sets of experimental 
conditions : the moist chamber and the open laboratory. It is possible 
by such a comparison to determine whether the rates of transpiration 
of the several species from different habitats stand in the same relation 
to each other under the Leeward Slope conditions of the laboratory 
at Cinchona and the Windward Ravine conditions of the moist chamber. 
This is best done by totaling the amounts of absolute transpiration 
for simultaneous periods and reducing the totals to the basis of the 
lowest as unity. Such figures have already been given for the labora- 



TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 105 

tory series with five species, and the figures are here repeated (table 
44) for comparison with the rates for the moist chamber series (table 43) . 
A comparison of the two columns of figures shows the first three 
plants to stand in approximately the same relation to each other under 
the two sets of conditions. The two ferns from the Windward Ravines, 
however, exhibit lower rates of transpiration in comparison with Pepe- 
romia basellcefolia, as well as the other species, under moist-chamber 
conditions. The significance of this fact is that the average play of 
atmospheric conditions in the laboratory at Cinchona was less humid 
than it is in the natural habitat of the two ferns, and they were con- 
sequently exposed to a water loss greater than that which would take 
place in the Windward Ravines. In other words, the two ferns were 
subjected to a greater acceleration of transpiration by removal from 
the rain-forest than were the other three species of the less humid 
habitats. Such behavior on the part of Diplazium and Asplenium is 
abundantly explained by the lightness of their epidermal water-con- 
serving structures. In none of the experiments with these species were 
they observed to wilt or show the least sign of loss of general turgidity, 
although such appearances could be readily secured by exposing them 
to half an hour of sunshine. The transpirational behavior of the ferns 
in the shade of the laboratory is, therefore, normal in its character, 
although the water losses are themselves higher in amount than in the 
Windward Ravines (see p. 67 and p. 76). 



GENERAL CONCLUSIONS. 

Jamaica presents typical insular tropical conditions, with a rainy 
windward coast, a leeward dry coast , and an intervening cool mountain 
region. The interesting changes of vegetation between sea-level and 
4.500 feet (1,370 meters) have been so seriously modified by human 
interference as to be only imperfectly recognizable. Above this ele- 
vation, however, is an almost unbroken cover of virgin vegetation, in 
which the floristie and vegetational changes are relatively slight from 
4.500 feet to the highest summit, at 7,428 feet (2,205 meters). This 
undisturbed montane region is characterized by a rainfall of from 105 
inches (268 cm.) to 168 inches (427 cm.), and by the prevalence of a 
cloud blanket which is particularly persistent over the windward slopes 
of the mountains. The prevailing vegetation is a type of rain-forest 
which possesses an intermingling of tropical and temperate character- 
istics, and a floristie admixture of genera from the adjacent lowlands 
and from the north temperate zone. 

Within the rain-forest region the major distinction of climate and 
vegetation is that which exists between the windward and leeward 
slopes of the main mountain mass, which lies nearly at right angles 
to the direction of the trade winds. On both sides of the mountains 
minor distinctions may be made between the vegetation of ravines, 
slopes, and ridges. The effects of rain, fog, and wind are modified by 
the erosion topography in such a manner as to make the Ravines the 
most hygrophilous habitats, the Ridges the least hygrophilous, and the 
Slopes intermediate between the two. The forests of the ridges are 
essentially alike on both windward and leeward slopes, but those of the 
"Windward Ravines and Leeward Ravines, as well as those of the 
Windward Slopes and Leeward Slopes, present substantial differences. 
The most important physical factor concerned in the differentiation 
of these habitats is atmospheric humidity, although this is, in turn, 
conditioned by the prevalence of fog. 

The Windward Ravines exhibit most strikingly the characteristics 
of the rain-forest, some of which are lacking in each of the other habi- 
tats. No one of the forest types occupying the five habitats may be 
looked upon as possessing a closer adjustment to its own complex of 
physical conditions than does any of the others. No one of the types 
can emerge from its own habitat, and under no possible physiographic 
change of the region can any one of these habitats come to occupy all, 
or even a preponderant part, of the region. In other words, there is 
no means by which it might be possible to fix upon any one of the five 
types as representing the so-called " climax" forest of the Jamaican 
montane region. 

106 



GENERAL CONCLUSIONS. 107 

The topography is of prime importance for the distribution of the 
vegetation, for it is the agency by which the physical conditions are 
given their local modifications, and these modifications are in turn 
responsible for the distribution of the forest types. Changes in the 
topography are active, through erosion, but their operation leaves the 
relief of the mountains essentially unaltered as they are gradually worn 
down. There is no respect in which the progress of physiographic 
change alters the adjustment of physical conditions or the distribution 
of the habitats, excepting perhaps the case in which a ravine may 
broaden and eventually become a part of the larger slope down which 
the ravine formerly drained. Although the eroding power of a heavy 
tropical rainfall is rapidly carrying the montane region toward base- 
level, the only discoverable outcome of the process is that the present 
vegetation, with all of its present habitat distinctions, will gradually 
be carried down to a level at which climatic changes will dominate the 
history of the vegetation. The existence of two small areas of alpine 
meadow on high peaks at the present time would indicate that such 
has been the fate of types of vegetation that formerly occupied the 
higher elevations. 

Any successional phenomena which might be discoverable in the 
montane rain-forests, whether due to such physiographic change as 
the merging of a maturing ravine into its mother slope or to such 
climatic change as would cause a relict alpine meadow to be invaded 
by forest, would in any case resolve themselves into a matter of the 
gradual change of vegetation in dependence upon a gradual change of 
physical environment. The relation of the old vegetation to its envi- 
ronmental conditions, and the relation of the succeeding vegetation 
to its environmental complex are both matters that would far outweigh 
in importance the floristic and ecological features of the succession itself. 

Under the conditions of equable temperature and abundant water 
supply which obtain in the rain-forest, there are no climatic checks 
to the continual activity of the plants. The annual periodicities of 
growth and flowering are, however, greatly diversified, there being 
unbroken activity in some species and a well-marked winter season 
of rest in others. It may be said, in general, that the former ^peeies 
are those of tropical lowland relationship and the latter an' those 
belonging to north temperate genera. It is to the inherited differ- 
ences of physiological constitution between these groups of plants tlmi 
we must look, by experimental means, to an understanding of their 
divergence of behavior under identical physical conditions. 

The rate of growth in the montane rain-forest region is much slower 
than it is in the vegetation of the lowland-. The uncoiling leaves <!' 
tree-ferns and the leaves of some of the large herbaceous ferns exhibit 
a rapid rate of elongation. The growth of leaves is moderately rapid 
in the shrubs and trees which are in continuous or nearly continuous 



108 A MONTANE RAIN-FOREST. 

activity, but is slow in the majority of common trees, including those 
which arc completely defoliated in the winter months. Extremely 
slow rates of growth prevail among the trees which possess the most 

sclerophyllous types of foliage, and also among the herbaceous f lowering 
plants of the forest floor. 

The normal daily course of weather conditions in the rain-forest region 
is such that the total daily water loss of all plants is extremely low. 
The trees and shrubs are capable of relatively high rates of transpiration 
in full sunshine, but there are few days in which these rates are 
maintained for more than three or four hours in the early morning and 
perhaps an additional hour or two in the afternoon. The hygroph- 
ilous plants of the floor of the Windward Ravine forest are incapable 
of withstanding insolation for more than one or two hours, even at 
high humidities, without wilting. When brought into the climate of 
the Windward Slopes these plants lose from 3 to 3| times as much 
water per unit area as do the herbaceous plants of the least hygrophilous 
habitat, the Ridge Forest. When placed in the moist atmosphere of 
their own habitat the Windward Ravine plants lose only 2 to 2\ times 
as much water as the plants of the Ridge Forest. The open mesophyll 
and thin epidermis of the hygrophilous ferns enables them to maintain 
surprisingly high rates of transpiration in the shade, in an atmosphere 
of very high humidity; the rates of water loss per unit area are only 
half as great in the herbaceous flowering plants of the Ravines and 
Slopes, and from one-third to one-fourth as great in the plants of 
Ridges and in the epiphytic orchids. 

The prevailing conditions of the interior of the rain-forest are inhibi- 
tory to transpiration and also to photosynthesis. The constant high 
humidities and the dull light which prevails may well be responsible, 
through these functions, for the prevailing low rates of growth. The 
lowness of the temperature w T ithin the forest, and possibly also its 
equable character, are also connected intimately with the slow opera- 
tion of the individual functions of the plant and with the cumulative 
effect upon growth. 

When the transpiration rates of rain-forest plants are converted into 
rates of relative transpiration, and thereby correlated with the pre- 
vailing atmospheric conditions which are the determinants of the rate 
of evaporation and are the chief external factors determining trans- 
piration rate, they are then found not to be low. The rates of relative 
transpiration in Jamaican rain-forest plants and in plants of the Arizona 
desert are found to be of the same general order of magnitude. This is 
merely saying that the rates of transpiration in the two regions are 
proportional to the rates of evaporation which prevail in them. While 
the plants of the rain-forest are capable of losing much more water per 
unit area than are the plants of the desert if the two kinds of plants 
are brought under the same conditions, it is nevertheless true that as 



GENERAL CONCLUSIONS. 109 

each set of plants exists, under its own climate, the desert plant loses 
far more water in transpiration per unit area than does the plant of 
the rain-forest. 

In the herbaceous plants of the rain-forest there is no correlation of 
stomatal openness and relative transpiration rate, at least during the 
morning and mid-day hours. These plants possess extremely thin 
epidermal structures, through which the loss of water in transpiration 
is found to be slightly greater than the loss through the stomata. The 
preponderance of cuticular transpiration is largely responsible for the 
fact that the total transpiration is extremely sensil ive to the prevailing 
evaporation conditions and is partially responsible for the facl thai 
the relative transpiration rate of these plants when placed in dark] 
is not lower than their rates in the light. 

The writer's interest in the behavior of rain-forest plants has centered 
in the most hygrophilous forms, but these must not be taken as typi- 
fying the vegetation as a whole. The difference between the climate 
in the interior of the forest and in openings in the forest and the dif- 
ference between the climate at the floor of the forest and in its canopy 
are as great as the normal difference between widely separated pla 
Corresponding with these differences of climate are striking differei 
in the character of the vegetation, both when the forest floor is con- 
trasted with cleared thickets and when it is compared with the fore-t 
canopy. The dominant trees of the best developed rain-foresi pcflfi 
very sclerophyllous foliage; the high epiphytes have coriaceous succu- 
lent leaves; below them are to be found the normal leaves of the larger 
shrubs; beneath these the thin leaves of the larger herbaceous plant - 
with an open mesophyll of several layers of cells; while in the lowesl 
and most shaded situations are to be found such small plants a- ]'< pe- 
romia pellucida, with a single layer of mesophyll cells, and the filmy 
ferns, with leaves which are a single layer of cells in thickness. This 
tremendous contrast between the members of the several layers of the 
rain-forest and the vertical differences of climate to which the contrast 
is chiefly due are both dependent upon the existence of the forest itself 
and the power which each stratum of vegetation has for the mainte- 
nance of the conditions which are vital to the plants of the next stratum 
below. The dominant trees and the high epiphytes are capable 
withstanding the water Loss t<> which they are subjected in the infre- 
quent periods of cloudless weather, without fog or rain and with abnor- 
mally low humidity; while the hygrophilous plants of the lowest stratum 
are protected from the full duration of the -try periods by the Bhade in 

which they are growing and by the slowness with which theenOimOUS 

quantities of moisture are given up by the soil, the rotting logs, the 

beds of mosses and hepatics, and the litter of fallen twigs and leaves. 

There is no type of vegetation in which may be found a wider 

diversity of life forms than exist side by Bide or one above the other in a 



Ml) A MONTANE RAIN-FOREST. 

tropical montane ram-forest. Together with the structural diversities, 
discoverable in the field or at the microscope, arc diversities of physio- 
logical behavior, discoverable by observation or experiment, and some- 
t imes correlated with the structural features. There are quite as high 
degrees of specialization to be found in the rain-foresl as may be sought 
in the desert. The prolonged occurrence of rain, fog, and high humidity 
at relatively low temperatures places the vegetation of a montane 
rain-forest under conditions which are so unfavorable as to be com- 
parable with the conditions of many extremely arid regions. The 
collective physiological activities of the rain-forest are continuous but 
slow; those of arid regions are rapid, but confined to very brief periods. 
In the regions of the earth which present intermediate conditions 
between those of the desert and the reeking montane rain-forest may 
be sought the optimum conditions for the operation of all essential 
plant processes. It is, indeed, in such intermediate regions tropical 
lowlands and moist temperate regions that the most luxuriant vege- 
tation of the earth may be found, and it is also in such regions that the 
maximum origination of new plant structures and new species has 
taken place. 



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