CHAP, i The Nature of Alternation of Generations 47 



At about the time at which our period opens, and while 

 Hofmeister was still engaged on the Vascular Cryptogams, 

 Pringsheim was at work upon the Algae, publishing a series 

 of papers in 1856 and 1858, in the course of which he 

 established that both Oedogonium and Coleochaete show 

 a curious behaviour on the part of the fertilized cell, in 

 that it does not at once produce a plant like the parent, 

 but that it gives rise either at once (Oedogonium), or with 

 but little vegetative development (Coleochaete), to asexual 

 reproductive cells. Pringsheim saw indeed in the body 

 proceeding from the zygote of the latter an approximation 

 to the sporogonium of the simplest of the Liverworts. He 

 established, too, that these phenomena are rare among the 

 Algae, and showed that the latter are often polymorphic ; 

 there is not a regular alternation of sexual and non-sexual 

 forms in their life-histories. 



Though the question seemed ripe for discussion about 

 1860, the subject was only occasionally pursued for some 

 years. The earlier writers did not shake themselves clear 

 from the doctrine of the alternation of vegetative and floral 

 shoots, which they tried to make the basis of a scheme 

 into which the new discoveries should fit. Moreover, the 

 true homologies of the stages in development were only 

 slowly recognized. 



In contradistinction to these somewhat nebulous views, 

 we find an important pronouncement made by Celakowsky 

 in 1868. He cleared the way for the discussion of the 

 whole problem by showing that the old alternation of 

 shoots stood quite apart from the new question, and how- 

 ever varied might be the forms involved, and whatever its 

 own intrinsic importance, it must be put quite on one side 

 when discussing the more far-reaching problem. 



Celakowsky accepted the discoveries of Hofmeister and 

 Pringsheim and their results as to the structure of the 

 archegoniate plants and the Thallophytes, and made them 



