TRANSACTIONS OF SECTION K. 763 



of the laterals leading to the typical dicotyledonous structure with a diarch root 

 first described. 



The evidence for this view of progressive reduction is primarily the prevalence 

 of the more complex types in the older Gymnosperms, but other considerations 

 that can be adduced in its support cannot be given in an abstract. The difference 

 between the more complex and the simpler types cannot be directly correlated 

 with habit, as might perhaps be thought ; since there are instances of the same 

 type occurring in allied species of totally different seedling-habit. The suggestion 

 is made that the reduction has been brought about by such factors as reduction in 

 the size of the seed, leading to the formation of a much smaller seedling with 

 smaller and shorter-lived cotyledons, in which the plumule develops soon and 

 rapidly, and the cambium becomes active in the hypocotyl and root at a very early 

 period. 



The level at which transition from endarchy to exarchy takes place is very 

 variable. It seems that a high transition, typical of Gymnosperms and very many 

 Dicotyledons, is probably primitive. The continuation downwards through the 

 hypocotyl of separate endarch collateral bundles of the cotyledon traces in a 

 relatively peripheral position, i.e., stem structure of the hypocotyl, has apparently 

 been acquired in a number of cases in which the hypocotyl projects considerably 

 above the ground, and early has to support a weight of foliage. 



4. The Seedlings of certain Pseudo- Monocotyledons. 

 By A. W. Hill, M.A. 



The majority of the dicotyledonous plants which are bulbous or geophilous 

 in habit possess some peculiarity in their method of germination, which is most 

 commonly of a monocotyledonous character. 



Certain bulhous and rhizomatous species of the genus Peperomia from the 

 mountains of South and Central America have pseudo-monocotyledonous seedlings. 

 They are, however, really dicotyledonous, but the behaviour of the cotyledons is 

 dissimilar. In the early stages of germination they both serve as absorbent organs ; 

 very soon one of them grows quickly and is withdrawn from the seed to serve as 

 an expanded assimilating organ, whilst the other remains within the seed and 

 never emerges, but serves to ahsorb the reserves stored in the perisperm. In 

 appearance the seedlings are monocotyledonous, and their method of germination 

 appears to be unique. This case suggests that evolution along similar lines may 

 have produced the normal seedling habit of such monocotyledonous orders as the 

 Aracece, Sue. ; for it is possible that the absorbent cotyledon and the so-called * first- 

 leaf ' may stand in the same relation to each other and be equivalent to the two 

 cotyledons of Peperomia. Some support is given to this view by the fact that the 

 cotyledon and first-leaf are directly opposite to each other in the Artcece. 



In the case of the genus Cyclamen there are some differences. Here the 

 embryo is truly dicotyledonous, but normally only one of the cotyledons is deve- 

 loped, and after serving as an absorbent organ it expands and becomes an assimi- 

 lating organ. The rudiment of the other cotyledon is always present and visible, 

 and it will usually develop into a normal green leaf should anything untoward 

 happen to the first cotyledon. In some species of this genus the second cotyledon 

 is Ibund to resemble closely the first cotyledon, whilst in other species it more 

 nearly resembles the ordinary foliage leaves. Some light may he thrown on the 

 origin of certain monocotyledons from a consideration of these anomalous dicoty- 

 ledons. It may be possible that the monocotyledonous mode of germination has 

 been evolved owing to the assumption of different functions by the two cotyledons, 

 in correlation with the adoption of the bulbous habit owing to adaptation to 

 xerophytic conditions. 



