144 HISTORY OF BOTANY 



life-histories of the Hepaticae and Mosses it is possible 

 to trace, with the greatest readiness, a progressive sterilisa- 

 tion of the sporocarp, starting with such a form as Riccia 

 and passing through Sphaerocarpus, Targionia, Marchantia, 

 Pellia, Anthoceros, and other genera, until we reach the 

 most highly elaborated sporocarps of the Mosses. While 

 in Riccia the great majority of the cells into which the 

 oosperm divides actually become carpospores or secondary 

 oosperms, in such a type as Pellia most of the products of 

 division are sterile and subserve other duties, such as 

 absorption, conduction, protection, dispersal, etc., and 

 only a comparatively small number are strictly repro- 

 ductive, although all the units may be regarded as 

 potentially sporogenous. That cells of these sterile 

 regions should under certain conditions produce proto- 

 nemata, as Pringsheim found, was thus only what might 

 have been expected ; the cells in question had recovered 

 their original sporogenous capabilities. 



Although this idea of progressive sterilisation in the 

 Bryophytic sporocarpia is the one almost universally 

 accepted, it should be borne in mind that other conceptions 

 of the phenomena are also held. Thus Goebel, in 1910, 

 put forward the view that the line of the Marchantiales 

 forms a reduction series, and that Riccia, instead of being 

 the simplest and earliest member of the group, is in 

 reality a reduced type. 



In the monographs to which I have referred Bower 

 examined in great detail the structure and development 

 of the sporogenous organs of all the chief genera of 

 Vascular Cryptogams and of many Phanerogams also, 

 with the view of establishing the occurrence of sterilisa- 

 tion of potentially sporogenous tissue throughout the 

 vegetable kingdom, and on the data he accumulated, 

 together with critical comparisons of the conditions 

 existing among the Bryophyta, he formulated his hypo- 

 thesis, which perhaps I may best give you in his own 

 words. 



