Evolution of Monocotyledons. 299 
dons and true Dicotyledons may be explained as having arisen as a 
result of such adaptation; for example, the presence of endosperm 
in the seed of most Monocotyledons is a character of highly 
specialised geophytes ; the distribution of vascular bundles in the 
stem and the loss of cambium in Monocotyledons may be ascribed 
to the shortening and thickening of the axis; the disappearance of 
the primary root and development of an annual crop of adventitious 
roots are clearly connected with the annual recurrence of a period 
of vegetative activity ; the form and venation of monocotyledonous 
leaves are the most suitable for insertion on the shortened axis and 
also for pushing up through the soil. The absence of a true epidermis 
on the root above the root-sheath 1 and the trimerous symmetry of 
the flower in Monocotyledons are points less easy of explanation, 
but in most respects, Miss Sargant’s theory is exceedingly well 
supported and shows that there is much to be said for the origin of 
Monocotyledons from a dicotyledonous race by Syncotyly, certain 
Liliaceae being considered to give the key to the situation. 2 
Compton (11, p. 800) from a study of teratological syncotyls 
amongst Dicotyledons, concludes that leaving the Spadiciflorae out 
of the question, syncotyly may well account for the origin of 
monocotyly in other Monocotydons. 3 He adds the following 
valuable observations to those of Miss Sargant:—With very few 
exceptions ( Sevvatula radiata, Limnanthes Douglasii, Cardamine spp. 
and possibly Megarrhiza californica (cf. Sargant 59, p. 83), species 
forming a cotyledonary tube have albuminous seeds, so that the 
small and usually straight embryo develops in a homogeneous 
medium, the endosperm, If syncotyly occurred at all, it would be 
expected to be symmetrical under these conditions—that is, to affect 
both edges of the cotyledons equally. On the other hand, species 
which are normally dicotyledonous but which occasionally produce 
syncotyls, are mostly exalbuminous, the exceptions being about one 
1 Cf. Henslow (31, p. 732). This author ascribes the absence of an epidermis 
to the degenerating influence of a moist or aquatic habit. 
2 With regard to the primitiveness of the Liliaceae, see also Lindinger (40), 
Lotsy (42), Hallier (28). Miss Sargant believes that aquatic Monocotyledons, 
such as the Helobieae, may be explained as having taken to an aquatic habitat 
in order to escape competition with the better-equipped Dicotyledons on land ; 
their characters must be regarded as secondary rather than primitive. Bessey, 
Wettstein and Warming, on the other hand, consider the apocarpous Helobiese 
to be the most primitive of Monocotyledons, a view indicated by Hallier in 1905 
(27) ; Lotsy also admits the claims of the group to primitiveness, deriving them 
from Pro-ranalean ancestors in common with the Liliiflorae. Nicotra (52) 
holds that the Cyclanthaceae are the primitive Monocotyledons. 
3 In this connection, it is interesting to note that Mottier (50) concludes, 
from his work on anomalous Dicotyledons, that the facts of their embryology 
“throw little or no light upon the relative antiquity of the two classes of 
Angiosperms ” (p. 460). 
