236 
two cotyledons. [ach trunk will produce many such “ flowers,” 
apparently simultaneously, since some fossil trunks show none and 
others several scores. The “ flowers”” shown are depicted with 
the whorl of * stamens ” expanded and unwithered. 
These Mesozoic cycad-like plants disclose many features which 
suggest that their ancestry is to be sought among the seed-ferns 
of the Paleozoic, and the resemblance of their so-called flowers to 
the flowers of such flowering plants as Magnolia has led some stu- 
ae 
dents to see in these Mesozoic forms the solution of that botanical 
riddie—the origin of the flowering plants. 
9. Angiosperms 
The true flowering plants appear in rather familiar forms during 
the later Mesozoic. They show a great modernization at the close 
of the Cretaceous, and the Tertiary is quite as much the Age of 
Flowering Plants as it is the Age of Mammals. Much of the 
geological history of the more familiar Temperate Zone tree genera 
is known. These are so like their ltwing descendants that there 
would be no point in preparing a transparency to illustrate them. 
Their chief interest is in the changes in distribution which they 
show, and the evidence which they furnish regarding changing 
environmental conditions, such, for example, as a wet delta forest 
in the Nubian desert in late Eocene times, or forests on the site of 
the Peruvian desert as late as Miocene time. 
There are numerous trees found in Europe at the beginning of 
the Pleistocene, such as walnuts, hickories, magnolias, and gums, 
which were exterminated on that continent by the Pleistocene Ice 
Sheets. Similarly, in North America there are present in the 
f other conti- 
late ‘Tertiary many genera which today are natives o 
nents, and many more, once found throughout our western states, 
but now confined to eastern Asia and southeastern North America. 
NOTE ON THE PREPARATION OF THE 
TRANSPARENCIES 
An exhibit of living plants, arranged to briefly illustrate the 
course of plant evolution from algae to flowering plants, was in- 
stalled several years ago in Conservatory House No. 2. Brooklyn 
