May 1900.] BOTANICAL SOCIETY OF EDIXBUHGH 297 



In answer to the query of what has caused these 

 variations, it may be submitted that the change in the 

 environment has acted as a variation-stimuhis. The 

 inherent tendency to variation may have been emphasised, 

 and the morphological results brought into marked promin- 

 ence by the cumulative influence of all the external 

 stimuli called into play by the sudden change in the 

 environment — the change from a life in the shade to a 

 life in the open, involving the free access of light and 

 air, as well as changed conditions of competition. In 

 addition, it is possible that a factor of some importance, 

 no doubt dependent on the former so far, is supplied 

 by the long inhibition of the reproductive functions and 

 the concurrent long duration of the purely vegetative 

 activity. 



Whatever difference of opinion there may be as to the 

 cause of these variations,' it may be admitted that they 

 are not without some interest when considered from the 

 point of view of descent, as bearing on the possible mode 

 of evolution of the Lycopodince from lower forms. 



" The study of variations," says Bateson (" Materials," 

 pp. 17 and 30), "offers a means whereby we Inay hope 

 to see the processes of evolution. In variation we look 

 to see evolution rolling out before our eyes." Again, 

 " the facts of variation must be the test of phylogenetic 

 possibility. ... If, therefore, we can see the variations, 

 we shall see the precise mode by which the descent is 

 effected." 



Viewed in this light, if these variations have any 

 meaning, it would appear to be that branching of the 

 strobilus and sterilisation of sporogenous tissues have 

 played a part in the evolution of the Lycopods. These are 

 two of the factors which Bower formulates in his " Hypo- 

 thesis of the Strobilus " (" Annals of Botany," vol. viii.) 

 to explain the mode of evolution of the sporophyte of the 

 Vascular Cryptogams from the simple sporogonial head 

 of the Bryophyta. Other two factors which have played 

 a part are, according to Bower, eruption of sporaugiophores 

 from a previously smooth surface, and relegation of sporo- 

 genous tissue to a superficial position. He shows how, by 

 agency of tbesp, the primitive strobilus of Phj/lJoglossutii 



THANS. BOT. SOr. EDIN. VOL. XXI. X 



