334 BOTANICAL GAZETTE [MAY 
They belong to eight genera which are systematically scat- 
tered, for they represent six families, Ranunculaceae, Fumariaceae, 
Umbelliferae, Primulaceae, Lentibularieae, Nyctagineae. Clearly 
these species cannot have inherited the peculiar form of their 
seedling from a common ancestor. It must be due to similar 
external conditions affecting certain species of very different 
descent in the same way. 
One feature is common to all the pseudo-monocotyledons 
in my list—they all possess some underground member which 
is thickened into a tuber. In Ranunculus Ficaria one of the 
earlier cauline roots becomes tuberous; in the other species the 
hypocotyl is more or less thickened. 
Moreover, the most complete list I can make of dicotyledons 
with their cotyledons partially united for some distance from the 
base. upwards includes twenty genera.*5 It contains but one 
genus — Rhizophora —in which the hypocotyl is not very much 
shortened, if not actually thickened. In the great majority the 
hypocotyl becomes a conspicuous tuber. The seeds of the single 
exception germinate under peculiar conditions, which would 
account for almost any amount of modification in the structure 
of the seedling. 
The association of a tuberous habit with the reduction of the 
cotyledonary members has been noticed by several observers. 
Darwin in the Movements of Plants? says: ‘From the several 
cases now given, which refer to widely distinct plants, we may 
infer that there is some close connection between the reduced 
size of one or both cotyledons and the formation, by the enlarge- 
ment of the hypocotyl or of the radicle, of a so-called bulb.” 
Now the formation of a shortened and generally thickened 
rootstock, whether morphologically a stem or a root, is charac- 
teristic of the plants which Professor Areschoug™ has called 
geophilous. Such plants are found in regions where the condi- 
tions during part of the year are unfavorable to vegetation. 
*SSARGANT, E., /, ¢., p. 73. 
*© KERNER and OLIveER, Natural History of plants 1: 602-4. 
7 DARWIN, C., The power of movement in plants 97. 1880, 
* ARESCHOUG, Beitriige zur Biologie der geophilen Pflanzen. Lund, 1896. 
