298 
N. Bancroft. 
donary fusion. The large number of Dicotyledons exhibiting cotyle¬ 
donary fusion indicates that it does offer advantages under certain 
conditions. 
What these conditions are is indicated at once by the fact that 
cotyledonary fusion is accompanied in practically all cases by 
shortened and thickened hypocotyls' (as in Eranthis), and by the 
formation of underground storage organs of some kind. The plants 
possessing these characteristics are geophytes, that is, plants whose 
aerial organs persist for a short annual season only, the underground 
parts forming a storage of food materials through the dead season 
(cf. Areschoug, 4, p. 1). The fact that most Dicotyledons exhibiting 
cotyledonary tubes are highly specialised geophytes suggests that 
fusion of the cotyledons is an adaptation to this habit. A consi¬ 
deration of the conditions under which a typical geophyte lives—for 
example, in Arctic regions, or on Alpine summits—makes it evident 
that its seedlings must be exceptionally well-adapted to their environ¬ 
ment in order to survive. By the end of the short period of growth 
the young seedling must be in a condition which will enable it to 
li ve during the adverse weather following ; so that at the commence¬ 
ment of the vegetation season it begins at once to form its 
underground organs. 2 “ In all cases however, the production of 
assimilating surfaces seems to be an object of secondary importance” 
and “ concresent cotyledons may be regarded as an adaptation for 
producing effective assimilating surfaces with the least possible 
expenditure of material. The production of a single cotyledon, 
whether by the more complete fusion of two or in any other way, is 
also an economy as compared with the formation of two cotyledons ” 
(59, p. 80). 
After a consideration of the above facts, Miss Sargant concludes 
that Monocotyledons have evolved through adaptation to ageophilous 
habit, an indication as to how this may have taken place being given by 
certain geophilous Dicotyledons which possess a single cotyledonary 
member. Many of the distinguishing features between Monocotyle- 
' The correlation of cotyledonary tubes and thickened hypocotyls has been 
noted by Sterckx (66, pp. 80, 81), Lord Avebury (Lubbock, 43, II, pp. 23, 24) 
and Darwin (13, p. 97). 
2 The behaviour of geophilous seedlings during the first season of growth 
falls into four classes : — 
i. The whole structure may remain underground —Megarrhiza californica 
and Arum maculatum. 
ii. The cotyledons only appear above ground— Eranthis hiemalis and 
Fritillaria imperialis. This is the most usual behaviour. 
iii. The cotyledons may remain underground in the seed, and the first leaf 
break through the soil— Anemone nemovosa and Eucomis nana. 
iv. Both cotyledons and foliage leaves come up above ground and act as 
assimilating organs— Delphinium nuAicaule. 
