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 twro visits to the Blue Mountains have been given to gaining
an acquaintance writh 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 showrn 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 wrell 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 wrhich 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 writh 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, wrhich 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 framewrork 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
ID1' 00" p. in.
55
50 :;
i> .;
»; 7
llh <)'>•" 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 :,
10h 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 "l»t 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 Volkens3
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 viewr 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 betwreen 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 wrindward 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 wrhich 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
•
_ • ■
•
0
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 1hi 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.
Schimper1 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.
2Shreve, 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 paper1 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 the1
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.
2Livingston, 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 Brown1 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 thermograph.
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 leewrard
side belowr 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 published1 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 wrere 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 wreek 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 twTo 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
1The 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
-
DO
"3
O
O,
_o
/.
-3
u
a
o
o
o
_g
'-,
u
rz
m
° <
— ■
Ml *"
I "3
3 Q
o a
>> o
; .-
° 5
e a
o
5 S
- B
^ §
- i-
-
- -
= ,3
SHREVE
Plate 28
-
CO
a.
<
a
u
o
5
c I
3
O
a
S
u
-7.
a .
- o
8 1
i s.
: a
5
a
-
a s
§ 8
1- ■
— ' I-
— 3
9 g
I g
= 2
- --z
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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 knowr 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. Lock1 found a rate of elongation of 231 mm. per day in the
shoots of the giant bamboo, Dendrocalamus, in Ceylon, and Maxwell2
observed a rate of 107 mm. per day in the growth of banana leaves.
Schimper3 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 exhibited rapid growth.
^ock, R. H. On the Growth of Giant Bamboos. Ann. Roy. Hot. Card. Peradeniya, 2, pt. -,
August 1904.
2Max\vell, W. The Rate of Growth of Banana Leaves. Bot. < Yntrl>., t'<7 , 1896.
3Schimper, 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 .
0 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 transpiration1 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 wras 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 wrere 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 wrater-tight joint wras 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 wrhich my potted plants were growing
wras 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.
9h30mp.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
'":35
.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 0 044 *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
":65
.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
':93
.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
3.46 921
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
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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 wrater-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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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
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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., wrhile 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.
Livingston1 has determined the rates of relative transpiration for
several desert annual plants, at the Desert Laboratory at Tucson,
Arizona, and Mrs. Edith B. Shreve2 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 wrork, makes
possible a comparison of the amounts and limits of relative transpira-
tion in plants of twro most wTidely 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 wrere 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 wrere made on small plants without leaves, and
on the twigs of trees, both with and without leaves, as wrell as on plants
growrn 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 wras carried on in the shade, with the
exception of that on Alchornea, Clethra, and Dodonaa.
1Livinston, B. E. The Relation of Desert Plants to Soil Moisture and to Evaporation. Carnegie
Inst. Wash. Pub. 50, pp. 45-65, 1906.
2Shreve, 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
0.182
1
....
....
1
.154
4
2
.141
3
0
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 9h 30m to 10h 30m 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 10h 30m to llh 30m (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 wTith 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.
TRANSPIRATION7 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 0
.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. .
9h00mp.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
5h 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
2h 15m 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 Comes1 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.)
5h25n
p.m.
8h 15m
llh 15m
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
4h 15m
p.m.
7h 15ra
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 positive1 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 wras 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
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., wfe
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 wras 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, then1 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 0 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*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
7b00ma.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 14.01M; 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 states1 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 reported1 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 showr 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 0 . 031
Average of 3 diurnal readings . 077
0 . 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
6h30mp.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.
9h 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
0 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 wTithin 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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