56 Proceedings 
cotyledons, In somne species however the cotyledons are 
united from the base upwards into a narrow tube which 
carries the two blades aloft. There are also a few species 
which have but one cotyledon. I have found references 
in botanical literature to above forty species in which 
cotyledonary tubes are formed, and about fourteen species 
in which the seedling of a Dicotyledon has but one coty- 
ledon. Omitting two species of Mangrove whose seedlings 
germinate under most exceptional conditions, all these 
aberrant Dicotyledons have one feature in common, Their 
main stem is subterranean with much shortened internodes, 
and is almost always thickened to form a tuber. They are 
in fact well-marked geophytes: that is, plants which live 
above ground for part of the year only. Their aérial mem- 
bers perish during the the winter, or in the periodical dry 
seasons of some hot countries, and while the conditions 
above ground are unfavourable the plant is reduced to an 
underground stem, provided with buds which will develop 
when the weather becomes genial. 
There are of course many geophytes with two cotyledons, 
but one feature is conspicuous in the seedlings of all such 
plants. They show very little green above ground in the 
first season. I have watched the germination of many geo- 
phytes. A few never come above ground at all in their first 
season. Some send up one cotyledon, some two: others— 
in which the cotyledons remain underground as sucking- 
organs—send up a foliage leaf or two, always very small. 
But they all form a squat colourless stem, generally tuber- 
ous, and sink it as deep as they can in the ground. 
The reason for this behaviour is very simple when we 
consider the climatic conditions under which such plants 
have been developed. The cold which forces the mature 
geophyte in Alpine or Arctic regions to take refuge under- 
ground during the greater part of the year, or the period- 
ical drought which has the same effect in many hot coun- 
tries, is still more formidable to its seedlings, The seedling 
which germinates at the beginning of a season of good 
weather, is inevitably killed off if it cannot protect itself 
against the long period of drought or cold which will follow. 
Sch y 
