298 THANSACTIONS AND PROCEEDINGS OF THE [Sess. lxiv. 



may have arisen from a simple sporogonial head ; and 

 how from such a simple strobilus, by sterilisation and 

 branching of the strobilus, the sporophyte of the hiyher 

 Lycopods may have been developed. " In the various 

 species of Lijcopodium!' he says ("Proc. Eoy. Soc," 1891-92, 

 p. 270), "the whole plant (exclusive of the protocorm) 

 represents an extended and branched form of such a 

 strobilus of which many of the sporophylls have been 

 sterilised and appear as the foliage leaves, having no 

 sporangia." Among other evidence from Lycopodiam 

 clavatum, he cites the fact that " arrested sporangia are 

 frequently present, and may be found either at the base 

 or the apex of the strobilus " (" Phil. Trans. Pioy. Soc," 

 vol. 185, p. 521). 



The variations described above go farther than this, 

 and their interest is therefore enhanced as beings extreme 

 cases confirmatory of this particular point in Bower-'s 

 theory. iSTot only do they show arrest of sporangia, but 

 they also demonstrate all the stages from partial to 

 complete sterilisation of the strobilus, with the passage 

 from sporogenous to vegetative tissue, as well as branclung 

 of the strobilus and incipient branching of the sporangia. 



Mehnert's(I) Principle ok "Time Displacements "(2) 

 applied to the development of tjif sporopuyte. by 

 J I,. A. PtOBEUTSON, :\r.A., B.Sc. 



(Head lotli May YMM).) 



It is admitted Ijy Ijiologists that Van Baer's principle of 

 biogenesis — the life history of the individual is a short 

 repetition of that of the race — does not hold good for 

 every type. 



Among highly specialised forms which are closely 

 related there may be very marked dillerences in the 

 development. New stages may be intercalated, others 

 may be passed through very rapidly, and others omitted 

 altogether. Organs which are more recent may appear 

 earlier in the ontogcmy tliaii others which are phylogen- 

 etically older. 'I'he developnicnt of the individual may be 



