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Full text of "A fossil flower"

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A FOSSIL FLOWER 










Published by 

FIELD MUSEUM OF NATURAL HISTORY 

CHICAGO 

1924 







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Field Museum of Natural History 

DEPARTMENT OF BOTANY 
Chicago, 1924 

Leaflet Number 5 

A FOSSIL FLOWER 

One of the last official signatures of President 
Harding was affixed to an act establishing the Cycad 
National Monument, the story of which forms an 
interesting chapter in the history of recent botanical 
science. 

The tract of land in the southern Black Hills of 
Dakota thus designated and now set apart "for all 
time" is neither especially distinguished for grandeur 
of landscape, magnificence of present vegetation, nor 
for other openly striking features. Nevertheless it 
is a place justly famous among botanists the world 
over. 

The locality had attracted attention nearly a cen- 
tury ago. In the course of the adventures related by 
Edgar Allan Poe in The Thousand-and-second Tale 
of Scheherazade, Sinbad and his companion encoun- 
tered an island "where the forests were of solid stone, 
and so hard that they shivered to pieces the finest- 
tempered axes. . . ." In a footnote to this tale there is 
mentioned by way of corroboration "the discovery 
of a completely petrified forest near the head waters 
of the Cheyenne, or Chienne River, which has its 
source in the Black Hills of the Rocky chain." 

That an unparalleled record of extinct life of the 
Reptilian Age lies imbedded in the rocks of this for- 
mation was scarcely suspected until about thirty years 
ago. It was not until then that the locality received 

[41] 



2 Field Museum of Natural History 

scientific attention 1 and some of its fossil tree 
trunks were described. They had been looked upon 
mainly as remains of fairly well-known cone-bearing 
plants, though among them had been noted stems, 
suggestive of both tree-ferns and so-called sago 
palms. These were determined to be fossil cycads 
of a type already known, especially in Europe, but 
more perfectly preserved than any hitherto seen. The 
fame of the locality, however, rests chiefly on the 
subsequent and surprising discovery that many of 
these fossil trunks bore actual flowers. These were 
brought to light by Professor Wieland of Yale 2 . 
Indicating that real floral structures had originated 
much earlier than had heretofore been supposed, 
these ancient and primitive flowers differ in many 
respects from those of the later true flowering plants 
and have proved to be botanically of extraordinary 
interest. 

The plants which bore these flowers flourished 
millions of years ago, 3 when egg-laying monsters 
were still extant. The common name "Cycadeoid" 

1. Professor Thos. H. Macbride of Iowa published the 
first description of a Black Hills cycad in 1893. Professor 
O. C. Marsh of Yale soon afterwards made a very extensive 
collection of the trunks. Professor Lester F. Ward made 
several reconnaissances of the region and described numerous 
species of these fossils. 

2. Less extensive material of similar kind in less per- 
fect stages of petrification had also been studied by European 
botanists, but without finality of results, when Professor G. R. 
Wieland in 1898 began his searching investigation of the 
Black Hills material, both in the field and laboratory. He 
was soon able to report surprising discoveries, and to make 
some of the most critical and important additions to paleo- 
botany, or the knowledge of ancient plants, in perhaps a gen- 
eration. 

3. The age of the formation in which they were found 
has been variously estimated. On the basis of the disintegra- 
tion rate of radio-active minerals it exceeds a hundred 
million years. 

The earliest known cycadeoid remains date from the 
Triassic, the latest from the Cretaceous. Their distribution in 
time thus covers the entire Mesozoic. The foliage type is 
even older. 

[42] 



A Fossil Flower 




Fig. 2. 

A LIVING CYCAD. 

(Dioon edule). 

The living cycads constitute a small and dwindling group, confined^ almost 
exclusively to the tropics. The "armour" formed by old leaf-bases remaining on 
the trunk, is a characteristic feature of the cycads, plainly to be seen in this fine 
photograph of a Mexican plant. 

Photograph by Professor C. J. Chamberlain. 



[43] 



4 Field Museum of Natural History 

meaning cycad-like, is from the generic name Cycade- 
oidea used about a century ago by the celebrated Dean 
Buckland 4 for specimens of their kind from the Isle 
of Portland on the south coast of England. The 
Cycadeoids are related to the living cycads which in- 
clude some so-called Sago Palms, and resemble them 
in stem structure and foliage, yet the presence of 
flowers places them in a separate group. Being en- 
tirely extinct, they are commonly and not incorrectly 
spoken of as "fossil cycads", as by using this term 
in a wide sense the cumbersome technical name is 
avoided. During the Reptilian or Mesozoic Age, the 
medieval era in the history of life on earth, the fossil 
cycads probably constituted at least a third of the 
vegetation. This age is therefore also known as the 
Age of Cycads. On the basis of its chief vegetation 
the succeeding Age of Mammals, which includes the 
present day, is characterized as the Age of the Flower- 
ing Plants. However, it was shown by Professor 
Wieland's investigations that the dominant types of 
the vegetation even in the mid-geologic era, had 
reached an actual flowering stage. 

Some plants of the Cycadeoid group were small- 
leaved and branched, and in general appearance must 
have been comparable to the simpler forms of modern 
trees. They were no doubt the very numerous for- 
est members of their kind. The great mass of the 
petrified forms which have been discovered were 
thick-stemmed, globular to low columnar plants, most- 
ly unbranched, though some are forked after the 
manner of cacti. They grew probably on the edge 
of deserts. 



4. English clergyman and geologist, author of the Bridge- 
water Treatise on Geology, Dean of Westminster. Buckland 
had advised with Robert Brown, the botanist, who suggested a 
family name, the Cycadeoidese. The term Bennettiteae is pre- 
ferred by some botanists. 

[44] 



A Fossil Flower 5 

Trunks of the thick-stemmed kind have been 
found in a few localities in Europe, in Afghanistan 
and in India. One such petrified stem, now in an 
Italian museum, was found in an old Etruscan necrop- 
olis or burial place near Bologna, where it had been 




•r— ." r ^L ^* 



Fig. 3. 

A FOSSIL CYCAD TRUNK. 

(Cycadeoidea dacotensis). 

Numerous large fructifications enclosed by their bracts are conspicuous 

among the pits which mark the ends of the leaf-bases. This magnificent silic- 

ified trunk was the first specimen described from the Black Hills. 

Courtesy of Professor T. H. Macbride. 

placed on a tomb by the Etruscans who obtained it 
from the near-by Apennine hills over four thousand 
years ago. About a thousand of these trunks have 
been discovered in the United States. The great mass 

[46] 



6 Field Museum of Natural History 

of them comes from the Black Hills of Dakota, the 
most numerous and important specimens being ob- 
tained from within the actual limits of the Cycad 
National Monument. Others have been found in Wy- 
oming, also in Maryland between the cities of Wash- 
ington and Baltimore, and isolated stems have been 
collected in Texas, Colorado and California. They 
were early recognized as fossils, although not always 
suspected to be plants. Their appearance is unusual 
and has attracted attention wherever they were found. 
The miners in the Potomac region kept them as curi- 
osities in their homes, regarding them as fossil bee- 
hives and wasp-nests. The workmen in the quarries of 
Portland, England, where they are encountered, long 
ago dubbed them "crows-nests." As in the cycads, the 
leaf bases in these plants remained after the foliage 
wilted down and now make up the outer layer, or 
"armour", of the trunks, at the surface of which the 
spirally disposed ends usually appear as depressions or 
pits. On this account the trunks were described by 
some early writers as petrified "masses of coral-cups" 
or as "clusters of barnacles." 

Professor Wieland found his fossil flowers secure- 
ly encased in this outer layer of the trunks. They 
were present mostly in the form of unexpanded buds 
but in many instances fruits had begun to mature. 
No actually open flowers have ever been found. Nat- 
urally any that were present when the chain of events 
leading to fossilization began, wilted and must have 
been quickly destroyed, as may be easily surmised 
after a glance at the delicate expanded structure. It 
was the fortunate preservation of the well-protected 
buds in a petrified state that made possible the inves- 
tigation of their nature. It is likely that these ex- 
tinct plants, like the century plant or the Talipot palm, 
flowered only once after a prolonged vegetative 
period, and then died down. The flowering must have 

[46] 



A Fossil Flower 




Figr. 4. 

A FOSSIL CYCAD IN FLOWER. 

This figure represents the conception of the famous paleobotanist, Nalthorst. 
The original painting is in the National Museum, Stockholm. 

Courtesy of Professor G. R. Wieland. 



[47] 



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Field Museum of Natural History 



been profuse, for some of the trunks preserved in the 
critical stage show upwards of five hundred buds. 
The position of the flowers on the old part of the 
trunk is unusual, but is not entirely unique, for a 
somewhat similar flowering habit is to be seen among 
some of the tropical forest trees. 




Fig. 5. 

A FOSSIL CYCAD FLOWER. 

(Cycadeoidea ingens). 

Photograph of the model in the Field Museum of Natural History. 

By the use of a tubular drill, Professor Wieland 
removed the buds and fruits from the petrified trunks. 
The cores thus secured were sliced and polished, so 
that the structures enclosed became plainly exposed 

[48] 



A Fossil Flower 



9 



to view. The preservation is often so perfect that 
microscopic details, such as pollen grains, may be as 
clearly observed as in living plants, and the study of 
an abundance of sectioned material has resulted in a 
clear comprehension of the structure. 

The most striking feature of one of these flowers 




Fig. 6. 

A FOSSIL CYCAD FLOWER. 

(Cycadeoidea ingens). 

Photograph of the model in the Field Museum of Natural History. Same as 
figr. 5, seen from above. 

is its branched stamens, which number a dozen or 
more, resembling the fertile fronds of certain ferns. 
The stamens are laterally united at the base and 
fused to a corolla-like "disk." The disk with the 

[49] 



10 Field Museum of Natural History 

stamens was thrown off as soon as the function of the 
latter was fulfilled. Similar but simpler disks had 
previously puzzled geologists who found them as 
detached specimens in various places. The center of 
the flower is occupied by a seed-producing cone, as is 
the case in the magnolias, especially in the tulip 
tree. In its minute structure the fossil cone is, 
however, quite different from that of these flowering 
trees, for the seeds are still naked instead of enclosed 
as in the present true flowering plants. Below the 
disks are numerous bracts, or "sepals", as they would 
be called in a modern flower. These constituted an 
outer protecting envelope which remained to surround 
the fruit as it matured. All the usual parts of a flow- 
er are seen to be present and disposed in the usual 
sequence. This fossil flower is thus unmistakably a 
flower according to all definitions — "the flower of 
Linnaeus, of Goethe, and of Payer", as their discov- 
erer states. 

It is quite natural to ask, what may be the con- 
nection between these ancient flowers and those of 
the modern flowering plants. 

The origin of the flowering plants proper is ob- 
scure. Their first appearance as leaf -impressions in the 
rocks dates from the latter half of the Age of Cycads. 
From the numbers and the considerable variety of 
their earliest traces, it is certain that they were then 
already far advanced. A long evolutionary history, 
which remains unknown, unquestionably lies behind 
their sudden rise to visibility. It was this late and 
apparently abrupt appearance of the flowering plants 
that was referred to by Darwin as an "abominable 
mystery." 

In the absence of fossil clues, the origin of the 
now dominant flowering plants is an unsolved prob- 
lem in spite of the intensive study of living plants that 
has been carried on for generations. Botanists are 

[50] 



A Fossil Flower 



11 



not agreed as to which of the many kinds of flower- 
ing plants may be assumed to be most primitive and 
to represent the nearest approach to an ancestral type. 
Indeed, botanical classification of the flowering plants 
is expressive of the uncertainty which prevails. 

Such being roughly the state of our knowledge 
— or ignorance — of the origin and primitive state of 
the true flowering plants, the question inevitably 
arises whether the ancient flowers of the fossil cycads 




Fijr. 7. 

A schematic flower of a hypothetical stock ancestral to 
cycads and flowering: plants. 

From Arber and Parkin. 

may not represent the ancestral type. The particular 
one described and figured here is considered much too 
specialized to be the ancestor of anything. It must 
rather be considered, with the plants to which it be- 
longed, to have been an end-product, or a final devel- 
opment in a vanishing line. However, some flowers 
of simpler fossil cycads of a less peculiar habit of 
growth have also been discovered. The degree of rela- 
tionship of the fossil cycads to the stock from which 

[51] 



12 



Field Museum of Natural History 



the flowering plants sprang has not been defined, but 
the consensus of opinion seems to be that the two 
lines are at best only distantly connected. The near- 
est relationship that appears to be possible is a con- 
nection by common descent from a still older group. 
Nevertheless it is difficult to escape the growing 
conviction that these fossil flowers shed light on the 
early floral structure of the true flowering plants. It 
is tempting to assume, at least by the way of hypothe- 




Fig. 8. 

A purely hypothetical primitive flower of the true 
flowering plants. 

From Arber and Parkin. 

sis, that the ancestors of these bore flowers organized 
on a similar plan. 5 The well-known English author- 
ity, Scott, thus says of the cycadeoid flowers, that they 
"for the first time brought the origin of the flowering 
plants within the range of scientific discussion." 

The alterations which would be required to trans- 
form the cycadeoid flower into that of the later flow- 
ering plant can easily be specified. Restorations of 



5. "The cycadeoid flowers show the possibilities and 
trends of variation and even the lines along which variation 
could primarily occur." Wieland. 

[52] 



A Fossil Flower 



13 



hypothetical ancestral flowers have been attempted 
by Wieland and others on this basis and visualized by 
the English botanists Arber and Parkin as reproduced 
in Figures 7 and 8. If their conception is accepted 
as correct in principle, the so-called "strobilus theory" 
of the flower becomes the only tenable one. Accord- 
ing to this the various parts of the primitive flower 
were disposed in the form of a cone, terminal on the 
flowering axis. Its seed-bearing members were placed 




Fig. 9. 
A TULIP-TREE FLOWER. 
The carpels are seen to form a strobilus or cone. In the magnolia the stamens 
are more numerous and arranged in a more definitely spiral manner. 
From Sargent. 

at the tip, followed in order by stamens and below 
these by the sterile members which are generally 
known as petals and sepals. The parts are assumed 
to be indefinite in number, and spirally arranged. The 
most primitive flowers, according to this theory, are 
those of the magnolia order, with the tulip tree flower 
approaching perhaps more closely than any other to 
the ideal type.* This well-known theory has long been 
entertained by many botanists who now find support 



Wieland, 1901. 



[53] 



14 



Field Museum of Natural History 



for their views in these fossil flowers. Others, more 
skeptical, refuse to attach any special significance to 
the older cycad floral type taken as a hypothetical 
"missing link." 




Fig. 10. 

Stages in the reduction of stamens from the frond-like condition 
in fossil cycad flowers (1. Cycadeoidea, 2. WiUiamsonia), through a 
hypothetical intermediate stage (3), to the condition in a flowering 
plant such as the morning-glory (4). 

From Wieland. 



The presence of the bell-shaped disk uniting the 
stamens has led to some speculation, particularly 
since it has also been found in another cycadeoid with 

[54] 



A Fossil Flower 15 

unbranched stamens. Professor Wieland 6 points out, 
that with the stamens reduced to simplest form, this 
disk or "campanula" would make a perfect corolla 
of the morning-glory type. The possibility is sug- 
gested that this feature may have been present also 
among some members of the primitive flowering stock 
and that the origin of the corolla of many flowers 
of the tubular type may be far more ancient than is 
is ordinarily supposed. Such are a few of the botani- 
cal questions which are raised. 

Entirely apart from their theoretical importance 
and possible bearing on the evolutionary history of the 
flowering plants, these early flowers are in them- 
selves objects of great interest. Considering the per- 
ishable nature of flowers and the delicate character 
of many of their parts, the fact of their perfect pres- 
ervation through millions of years seems remarkable. 
To bring to light and to restore with confidence ex- 
tinct flowers which bloomed at the time when the 
earliest birds were learning to fly is no small achieve- 
ment. The published results of Professor Wieland's 
investigations fill two large illustrated volumes issued 
by the Carnegie Institution of Washington, and a 
third, of equal interest, published by the Geological 
Institute of Mexico. 

Realizing the desirability of conserving the site 
that yielded these fossil trunks, Professor Wieland 
had the foresight to secure its immediate protection by 
filing a homestead claim to the tract of 320 acres. It 
is due to his initiative that this tract, which he later 
released for the purpose, is now preserved as a Nat- 
ional Monument of unique botanical interest. 

A reconstruction or model of this fossil flower 
as restored by Professor Wieland has been produced 
with his cooperation in the Stanley Field Laboratories 



6. Wieland, G. R., Botanical Gazette, Dec. 1909. 

[55] 



16 Field Museum of Natural History 

of the Field Museum of Natural History. It will be 
placed near the modern cycads in the hall devoted in 
this Museum to a synopsis of the plant-life of the 
world. 

B. E. Dahlgren. 



Fossil Cycad trunks and leaves are found in the ex- 
hibits of the Department of Geology in the west hall (Hall 
38) on the second floor. 

In the Department of Botany the Cycads are to be seen 
in the Hall of Plant Life, in the east hall (Hall 29), also on 
the second floor. 



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