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 Pringsh. Jahrb., Bd. ix., 1878, also Scott, British Association Report, Liverpool, 1896. 
Address to the Botanical Section. 
