THE 
NEW PHYTOIiOGIST. 
Vor,. VIII., No i. January 31ST, 1909. 
A THEORY OF ALTERNATION OF GENERATIONS IN 
ARCH EGON I ATE PLANTS BASED UPON THE ONTOGENY. 
By William H. Lang, M.B., D.Sc., 
Lecturer in Botany in the University of Glasgoiv. 
I T is difficult to overestimate the importance of the regular 
succession of two generations, differing both in their vegeta¬ 
tive and reproductive parts, in all plants from the Bryophyta 
upwards. The clear recognition of this by Hofmeister rendered 
possible the accurate study of the morphology of these plants and 
we are now in possession of the main descriptive facts regarding 
the life-histories of nearly all the groups. A copious literature has 
also accumulated on the nature of this alternation of generations, 
and the proper understanding of this must have a far-reaching 
influence on morphology as it passes from the purely descriptive 
stage. 
I do not propose to summarise here even the most recent 
works dealing with the nature of alternation. In his address to the 
Botanical section of the British Association in 1896, Scott re¬ 
stated the theory of homologous alternation of generations; he 
held this to he another hypothesis “ equally worthy of verification ” 
and an alternative to the antithetic theory of Celakovsky and 
Bower. Since that date a number of investigators have discussed 
the nature of alternation, and advanced views as to its origin. 
The names of Campbell, Coulter, Klebs, Potonie, Hallier, Lignier, 
Tansley, Schenk and Goebel may be mentioned without citing the 
literature in detail. We may, however, recognise several broad 
lines on which speculation has proceeded. 
