3 oi 
Evolution of Monocotyledons. 
while the other cotyledon—the apparently lateral ‘first-leaf’—is 
left to develop from its rudiment outside the seed (cf. Text-figs. 8 
and 9, p. 420)” (32, p. 422). Indeed, as Lotsy’s subdivisions of 
heterocotyly suggest, this series may end in monocotyledonous 
cases, where the second aerial cotyledon is completely disguised as 
the first leaf (42, p. 624). 
Further, Hill thinks it is possible that the median bundle of the 
single seed-leaf of some Monocotyledons has become divided in 
more advanced types, such as Anemarrliena (considered by Miss 
Sargant to be primitive), this being correlated with the parallel 
venation of the leaves of the Liliacese (32, p. 423). In opposition to 
Miss Sargant, he considers the type of anatomy in an Arum seedling 
as being more primitive and near dicotyledonous ancestors (such as 
Piperaceas), and the Anemarrliena type as derived through such 
simpler Liliaceous forms as Zygadenus. 
Lotsy is in complete agreement with Hill in regarding the 
Spadiciflorae as an example of heterocotyly. As may be seen from 
his phylogenetic scheme (Diagram IV), he derives them from 
ancestors near the Piperales. Compton also apparently agrees 
with this view (11, p. 801) 1 . 
The second kind of heterocotyly is that in which reduction or 
even complete suppression of one cotyledon has taken place. 
Lotsy quotes as an example of reduction .of one cotyledon the 
embryo of grasses, in which the scutellum functions as an ordinary 
suctorial cotyledon, while the epiblast is considered as representing 
the reduced second cotyledon. This view was put forward by 
Mirbel in 1810 (49, p. 424 in note), and some twenty years later, as 
we have seen, Agardh (1, p. 197) held that Grasses were the only 
true Monocotyledons because one cotyledon had become completely 
suppressed. As Compton points out in his recent paper (11, p. 800), 
it is unsafe to theorise about this case, for there still exists too 
great diversity of opinion as to the morphology of the grass embryo. 
The chief supporter of the suppression theory is Henslow (30, 
31), whose papers in 1892 and 1911 bring forward evidence, partly 
from experiments on land and water plants, in support of his 
contention which may be stated briefly as follows:—Monocotyledons 
and Dicotyledons come from a common dicotyledonous stock, mem¬ 
bers of which gave rise to true Dicotyledons or to Monocotyledons 
1 From a study of the morphology of germination, Gatin (24, p. 54) con¬ 
cludes that there is not sufficient evidence for the adoption or rejection of Hill’s 
theory. 
