352 Bower . — On antithetic as distinct from 
goniate series, in which the progress of the sporophyte from 
a minute, indifferentiated body to the large independent plant 
may be followed ; and though the evidence concerning the 
evolution of the Archegoniatae must naturally fall short of 
actual demonstration, it is at least sufficiently satisfactory to 
substantiate the view that the sporophyte is a result of inter- 
polation of a new stage between successive gametophytes, 
rather than a result of formal modification of the gametophyte 
itself 1 . 
Accordingly it may be concluded that in the first and most 
prominent case of alternation of generations (that in fact 
which is recognised by botanists as par excellence the typical 
alternation) the origin of the alternation may be correlated 
with a change of habit from aquatic to sub-aerial life, and the 
neutral generation or sporophyte may on phylogenetic grounds 
be viewed as an interpolation of a new, and essentially sub- 
aerial phase between successive gametophytes : we will next 
enquire whether any other type of alternation, differing in 
nature or in origin, occurs among other plants. 
On this point we find in the Text-book of Sachs 2 a direct 
expression of opinion : it is there stated that a comparison 
of the development of the Thallophytes with that of the 
Muscineae and Vascular plants will show ‘ that the development 
of all plants which possess sexual organs may be divided into 
two stages which correspond in all essential points to the two 
generations in the life-history of a Fern : and that there is, 
therefore, in the whole vegetable kingdom only one type of 
alternation of generations so far as it is brought about by 
sexual organs.’ In his later published Lectures Professor 
Sachs does not materially alter this opinion. In the same 
year as the above passage was published, Celakovsky had how- 
ever given an address 3 on alternation, which states very clearly 
the reasons for his drawing a distinction between different 
types of alternation ; the chief point which he there insisted 
1 This view is clearly stated by Naegeli, Abstammungslehre, pp. 474, 475. 
2 Second English Edition, p. 229, or fourth German Edition, p. 234. 
3 Sitz. d. k. Bohm. Ges. d. Wiss., March 6, 1874. 
