SEXUALITY IN PLANTS—JOHNSON. 405 
reduction evidently follows immediately in the next developmental 
phase, when this spore germinates to form the sporidia. In the toad- 
stools, according to Wager (1893), Dangeard (1894), Harper (1902), 
Nichols (1904), and Levine (1913), the fusion of nuclei occurs in the 
basidium, and the reduction at the very next division of this fusion 
product, when the four spore nuclei are formed. 
The striking uniformity with which the apparent reduction occurs 
in all Basidiomycetes, at the time of formation of the sporidia or 
basidiospores, affords good evidence that this type of spore formation 
is a long-established one, common to the whole group. It thus sup- 
ports Brefeld’s view that the promycelium of the smuts and rusts is 
homologous with the basidium of the higher forms. That the point 
in, the life cycle where the associated nuclei finally fuse is the point at 
which it occurred in the earliest Basidiomycetes is not so clear. The 
modes of bringing about the first association of the paired nuclei are 
so varied that it is difficult to detect any clearly ancestral type among 
them all. The structures concerned with this process in the scidium- 
forming rusts certainly seem most readily comparable with the repro- 
ductive organs of other thallophytes. It seems probable that the 
occurrence of fusion at the same point im all forms is due to its being 
postponed in all forms as long as it could be, without being pushed 
over into another phase of the life cycle. 
It would be instructive to spend another half hour, as we can not 
do here, in considering those peculiar short cuts in reproduction 
known as apogamy and apospory. These phenomena are so patently 
secondary and so relatively infrequent that they can not be looked to 
for evidence of fundamental importance concerning the history or the 
significance of the essential sexual process itself. Their study has, 
however, served to correct certain false assumptions concerning the 
relation between the difference in chromosome number and the differ- 
ence in structure of the two generations. For example, the apoga- 
mous production, by Nephrodium molle, of a normal fern sporophyte 
with the X number of chromosomes demonstrates as no other kind 
of evidence could that De Vries was right in regarding the normal 
sporophyte as really two beings in one. Incidentally too, such phe- 
nomena suggest how comparatively unimportant it is for the structure 
of the plant, in what manner, and at what point in the life history the 
association of the 2X number of chromosomes is brought about. 
CONCLUSION. 
In our rapid glance at the progress made in the study of this prob- 
lem during 20 centuries we have seen how for 18 centuries men at- 
tempted to solve the problem by recourse to philosophical reasoning, 
without the aid of detailed observation or experiment. Then, in less 
than 2 centuries, by the use of these means, Camerarius proved that 
