56 riluCEEKINGS OF THE 



gaineto|tli\iic similarities fiiii to be fouviiiciiijj;. Ilcrc, I lliiuk, 

 we nu'rely have superficial reseniblances of no phyletic si<;iiificance. 



Both Poarsoii (39. pp. 334 & 340) and Thompson (55. p. 150) 

 are inclinetl to regard the terminal (cauline) ovule as primitive 

 and raise anew what we had hoped was an out-of-date controversy. 

 On the stro])ilus theory the cauline ovule presents no puzzle. 

 Primitively from Pteridosperms onwards the ovule was leaf-borne. 

 In the case of a pro-anthostrobilus in which both carpels and 

 ovules have been reduced to unity and the carpellary-leaf to 

 vanishing point, then through stress of circumstances the solitary 

 ovule becomes pressed into the terminal position and may for 

 descriptive ]iurposes he termed cauline. It occuiiies the place of a 

 terminal hud, but it cannot be considered as such, nor can it be 

 regariled phyletically as of cauline origin. Such reasoning applies 

 to the solitary terminal ovule of the Gnetales. ]n the Angio- 

 spermous flower a terminal cauline ovule can result from a 

 syncarpous gyncecium becoming reduced to a single ovule, but in 

 this case naturally some carpellary structure remairis to enclose 

 the developing seed. 



T/ie Anr/iospfrms a nwnophi/letic nroiip. The writer is under the 

 impression that at the present time the majority of botanists 

 regard the Angiosperms as a natiu'al, that is to say a nionophyletic, 

 group. This view has only become ])revalent in recent years. 

 As late as I'Jll Prof. Weiss favoured a polyphyletic origin 

 (57. p. o5()). 



Notwithstanding the wide differences in floral structure the 

 two following sti'iliing features render to my mind the monophy- 

 letic standpoint w eil-nigh unassailable : — 



(1) The stereotyped nature of the embryo-sac. 



(2) The same type of microsporopliyll throughout the group. 

 Even admitting the possibility of the Angiosi)ermous embryo- 

 sac as having arisen indejjendently more than once, the chance of 

 its being associated each time with the same kind of microsporo- 

 phyll would be extremely unlikely. 



The monophyletic view could be based on other grounds, such 

 as vascular anatomy. ]{especting those touching the flower, 

 the acceptance of the Eanalian hypothesis would be involved. 

 Let the monophyletic origin be conceded, then the only 

 rational way of explaining the evolution of the flower is by this 

 liyj)othesis. 



Amentifero-. Those botanists who reject the application of the 

 reduction theory to the flower of the Amentiferaj appear to be on 

 the horns of a dilemma. They must either accept a polyphyletic 

 (or at least a iliphyletic) origin for Angiosperms, or else must 

 show how to derive the bisexual from the unisexual flower. 



What evidence is there for the view that the hermaphrodite 

 flower has evolved from the unisexual one? Professor Weiss 

 rejects the application of the reduction idea to the Amentnles 

 on account of this grouj) possessing " certain characters w hich 

 npi)ear to mo to be undou!)tedly primitive '' (57. p. oo^:). The 



