CHAPTER VI. 



THE BIOLOGICAL ASPECT OF ALTERNATION. 



THE phenomenon of Alternation of Generations may be viewed in 

 various ways, and the history of the science shows that the different 

 aspects of this subject have presented themselves in a natural succession 

 according to the progress of biological thought. First it seemed sufficient 

 merely to observe the fact that successive, more or less distinct phases 

 occur in the life of the individual in certain groups of plants. In the 

 case of the Pteridophytes this was the gradually achieved result of the 

 labours of various workers antecedent to or contemporary with Hofmeister ; 

 but subsequently the discovery of a similar succession of phases in other 

 organisms than those in which it was first observed suggested at once their 

 comparison : such comparison was placed upon a secure footing for 

 Archegoniate plants by Hofmeister himself. Then followed the pursuit 

 of such comparisons into the region of the lower and simpler Thallophytes ; 

 but this led to some confusion at first, owing to premature attempts to 

 reduce all organisms which show sexuality to one rigid scheme as regards 

 the successive phases of their lives. On the other hand, in similar com- 

 parisons with the higher Flowering plants, the issues were temporarily 

 obscured by discussions over " the Alternation of Shoots " found in some 

 of them, and by the confounding of this with Alternation of the more 

 fundamentally distinct Generations seen in the Archegoniatae. But these 

 temporary clouds were in great measure cleared away by Celakovsky, when 

 he drew the distinction between "Homologous" and " Antithetic" Alterna- 

 tion. His comparisons, however, were still, like those of Hofmeister and of 

 Sachs, based essentially on form ; nevertheless, he arrived at conclusions which 

 we have seen in a previous chapter to coincide very nearly with the opinions 

 current at the present day, and this notwithstanding that those opinions are 

 now based on facts which were quite inaccessible to him. The writings of 

 Celakovsky may be said to have brought the formal study of Alternation to 

 a close. His conclusions were widely accepted at the time, though Botanists 

 of the weight and standing of Pringsheim still stood aloof from them. 1 



1 Pringsh. fahrb., Bd. ix., 1878, also Scott, British Association AV/wY, Liverpool, 1896. 

 Address to the Botanical Section. 



