C titter ia multi fid a ( Grev .). 103 
northern waters is associated with a correlative diminution 
of the now useless male organs ; so that, under extreme 
conditions, the admittedly asexual mode of reproduction 
alone remains on the perennating form. There can thus be 
little doubt that in the case of Gijfordict and the Tilopterideae, 
purely morphological considerations may be a better guide 
to the theoretical degree of sexual specialization than the 
physiological observation of the act of fusion of the gametes ; 
and further, that until more complete physical data are 
forthcoming as to the exact conditions of the experiment, 
a single positive result must far outweigh many negative ones, 
and the evidence that the so-called plurilocular sporangia of 
the Phaeosporeae are not potentially gametangia remains 
inconclusive. 
Nor, on the other hand, do the data for Cutleria point so 
much to an imperfectly differentiated or incipient sexuality, 
as to an actual and progressive loss of that function ; and thus, 
by analogy, the conception that the primitive Ectocarpus-Ytke 
ancestor of the Phaeosporeae was a sexual plant with iso- 
gamous gametes would be strengthened rather than under- 
mined. At any rate it is clear that the actual data for any 
given plant can only be obtained by actual observations 
taken at different times of the year at different points of 
distribution. 
Phylogeny of Cutleria. 
All generalizations as to the phylogeny of existing Algae 
must, in the present state of our knowledge, be necessarily 
more or less founded on the very hypotheses the scientific 
botanist most desires to prove. At the same time the only 
proof of such hypotheses at present attainable consists in their 
complete agreement with ascertained facts ; and thus so long 
as the tentative character of the proceeding is clearly borne 
in mind, it may become of interest to construct a phylo- 
genetic scheme for the life-history of the genera Cutleria and 
