Anatomy of Teratological Seedlings . IV. 485 
terizing forms like Anemarrhena. There is no evidence, however, of any 
connexion between the absorptive cotyledonary function and the separation 
of the halves of the ‘ double ’ bundle, and in the absence of such evidence 
this idea can only be regarded as purely speculative. It has been pointed 
out already that the orientation of the epicotyledonary leaves presents 
a difficulty against which this theory has to contend, and it is noteworthy that 
in Impatiens Roylei undoubtedly syncotylous seedlings exhibit that balance 
of cotyledonary structures and first epicotyledonary leaf which Hill has 
laid stress upon in certain Aroids (e. g. Arisaema dracontium). Apart from 
this, however, there seems to be no reason to consider Hill’s view as unlikely, 
nor does its acceptance automatically eliminate the possibility of a syncoty- 
lous origin for some groups of Monocotyledons. Certain systematists, 
notably Lotsy, would regard the Monocotyledons as at least diphyletic in 
origin, deriving the Spadiciflorae from an ancestral dicotyledonous group 
approximating to the Piperales, and the remaining forms from a hypothetical 
pro-ranalean stock which has also given rise to the modern Ranales. The 
derivation of the Monocotyledons from the Dicotyledons by the complete 
suppression of one cotyledon depends for support largely on indirect 
evidence. Many undoubted Dicotyledons are known in which there occur 
seedlings showing a marked dissimilarity in size between the two cotyledons 
(e. g. Abronia spp., Citrus Aurantium , Pachira aquatica). Occasionally 
a similar phenomenon occurs in Impatiens Roylei , and the anatomy of three 
such seedlings has already been described, two in the present and one in 
the previous paper (18). Other Dicotyledons, again, are known in which 
only a single cotyledonary member is produced normally (e. g. Cyclamen 
persicum , Ranunculus Ficaria , Carum bidbocastanum , Corydalis tuberosa). 
Of the first group Abronia umbellata , A. villosa (17), and Impatiens Roylei 
are, as far as can be ascertained, the only species in which the anatomy has 
been investigated. These undoubtedly show that where a pronounced 
inequality in the size of the cotyledons exists this exercises a marked effect 
on the vascular symmetry of the hypocotyl and, in a measure, of the root, 
the strands contributed from the smaller cotyledon being less important 
than those of the larger one. With regard to the pseudo-monocotyledonous 
types the available evidence, though as yet somewhat meagre, points to 
their being syncotylous in origin in many cases (32). The all-important 
cases which link the species with unequal cotyledons with those which are 
apparently pseudo-monocotyledonous are thus lacking, and in their absence 
the ‘ suppression ’ hypothesis must be regarded as not proven. 
The most recent theory as to the origin of the Monocotyledons is that 
put forward by Coulter and Land (8), who consider that there exists both in 
the Monocotyledons and Dicotyledons a peripheral cotyledonary zone which 
gives rise to two or more growing points or primordia, this being followed 
by a general zonal development and resulting in a cotyledonary ring or 
