248 
F. E. Fritsch. 
In the case of the more advanced Florideae, several of which 
have been fully studied, 1 we have the most complicated instances of 
alternation known among the Algae. We may take Polysiphonia as 
a type. Here we have first the production of a phase, which arises 
by the elaboration of the zygote and is constituted by the cystocarp. 
The carpospores of the latter give rise to a Polysiphonia, identical 
in all respects with the thallus bearing the sexual organs, except 
that it is diploid and produces only tetraspores. The latter again 
give rise to the sexual Polysiphonia, reduction having taken place 
during the tetrad-division in the tetrasporangium. 2 The numerous 
complications occurring in many forms and disclosed by the work 
of Oltmanns and others can be neglected here, where we are only 
concerned with the main facts. 
In the life cycle of these Florideae we therefore have two 
spore-bearing generations, viz., (a) the cystocarp, parasitic on the 
gametophyte and propagating by carpospores ; and (b) the ordinary 
Polysiphonia, independent and propagating by tetraspores. That 
reduction, which can only take place once in such a life-history, 
occurs on the second spore-producing generation is probably 
associated with the acquisition of a definite tetrad-stage in spore- 
formation (p. 11 ). The writer would regard these advanced 
Florideae as exhibiting both an antithetic spore-producing generation 
and one which is strictly homologous. 3 If, as he has attempted to 
show, both antithetic and homologous alternation can occur among 
the Algae, it is quite plausible that the two phenomena should be 
combined in the same life-cycle. 4 
Amongst all the cases of alternation among Algae that have 
been considered, that of Cntleria certainly stands out as the most 
illuminating in connection with the main theory here propounded. 
Though the result in this case is just the opposite, viz., a prostrate 
sporophyte and an erect gametophyte, it fully illustrates the course 
of events here suggested. 
In conclusion, some of the main features may be briefly 
summarised as follows :— 
1 cf. Yamanouchi, in Bot. Gaz. XLI, 1906, p. 425 and XLII, 1907, p. 401 ; 
Lewis, in Ann. of Bot., XXIII, 1909, p. 639 ; Svedelius, in Svensk. Bot. Sidsskrift 
V, 1911 ; VI, 1912; VIII, 1914 ; also Ber. deutsch. bot. Ges. XXXII, 1914. 
3 cf. Yamanouchi, loc. cit. 
5 The strict homology of the sexual and tetraspore-bearing generations is 
shown by the occurrence of abortive tetrasporangia on sexual plants and of 
abortive carpogonia on tetraspore-bearing plants ; for details, see Svedelius and 
Lewis, loc. cit. 
* cf. also Tansley, in New Phytologist, XI, 1912, pp. 213—216. 
