468 THE AMERICAN NATURALIST. [Vov. XXXIX. 
smuts and of yeast cells, the fusion of nuclei in the teleutospore 
and basidium and in the apogamous development of ferns, the 
© 
double fusion of polar nuclei and multiple nuclear fusions in the 
embryo-sac (Corydalis) illustrate phenomena which I cannot 
regard as sexual eyen though they have in them elements asso- 
ciated with sexual processes and in certain cases may be substi- 
tutes for a former sexual act. In none of these instances can 
we be positive that the nuclei concerned are morphologically and 
phylogenetically gamete nuclei. This point was discussed in 
some detail in Section IV. It seems to me that Blackman’s 
(:04a, p. 353) conception of the cell fusions preceding the æci- 
dium in Phragmidium as “reduced forms of ordinary fertilization " 
or Farmer's (:03) explanation of apogamy in the fern “as a kind 
of irregular fertilization" leads to a confusion of a substitute 
process with a true sexual act. The substitute processes have 
their true place as phenomena of apogamy. They can, however, 
only have a sexual significance if they represent the origin of a 
new set of gametes in the organism, a proposition which is not 
likely to be maintained by anyone. 
3. SPOROGENESIS. 
We are employing the term sporogenesis, as must have been 
apparent in preceding divisions of this paper, to designate a 
characteristic and highly specialized type of spore formation that 
is universal in all plants above the thallophytes. The process 
always terminates the sporophyte phase in ontogeny of these 
higher plants, and is especially distinguished as the period of 
chromosome reduction in the life history. The cell activities of 
sporogenesis are therefore of particular interest, and, since spore 
mother-cells are generally large and their nuclear and cytoplasmic 
structure especially clearly differentiated, we have perhaps ob- 
tained more knowledge of mitotic phenomena from the study of 
these elements than of any other tissues of the plant body. 
t The reduction phenomena of sporogenesis have been estab- 
lished in some forms of the thallophytes, certainly in the tetra- 
spore mother-cell of Dictyota (Williams, :04a). There are also 
reasons for suspecting that the oóspore of CEdogonium and the 
