Rickett.—Fertilization of Sphaerocarpos . 
249 
Time Relations. 
Mention has already been made of the fact that sporophytes become 
large enough to be readily visible from two to eight weeks after flooding. 
This indicates that the speed of the process of fertilization and the rate of 
development of the embryo may vary under different conditions or in 
different cultures. The cultures that took the longest time (eight weeks) to 
produce visible sporophytes were those from which Series C was made. 
This fact coincides exactly with the cytological data, for, although the 
fixations in this series were carried on until 66 hours after flooding, no stages 
were found farther advanced than Phase 5, while in the other series fixa¬ 
tions made 60, 64, and 65^ hours after flooding disclosed many examples 
of Phases 6 and 7 (Table I). 
The earlier stages seem to proceed at a quite uniform rate, so that it is 
possible to assign definite time limits to the first three phases. Phase 4 
shows considerable variation; and Phase 5 still more. Finally, Phase 6, 
which includes the actual division of the fertilized egg, seems to occur over 
a wide range of time. It is also noteworthy that the preceding phase (5) is 
quite prolonged, as though the changes that go on therein require a long 
time for their completion, while the division itself is rapid. It is evident 
that, after a long period of slow and gradual change, during which time the 
egg nucleus organizes its chromosomes, the egg cytoplasm takes on 
a definite structure, and the male nucleus is in a condensed state, the 
further processes leading to the first division—the formation of chromosomes 
by the male nucleus and the disappearance of the nuclear membranes—take 
place with almost explosive suddenness. Furthermore, the time necessary 
to complete the slow preliminary changes and to initiate the actual division 
varies very greatly with the individual. These time relations are illustrated 
(Table I) by the small number of cases of Phase 6 as compared with the 
number of cases referable to preceding and succeeding phases. This is not 
because fewer slides were made covering this time, since the instances ot 
Phase 6 that were found occurred often at the same time, sometimes on the 
same plants as afforded numerous instances of Phases 5 and 7. 
A few antherozoids are often seen in the cavity of the venter outside 
the egg in later stages, when fertilization has already taken place. These 
retain their normal form, and to all appearances were alive at the time of 
fixation. This fact suggests the possibility that some of the variation in 
time of the different stages in fertilization may be due to a variation in the 
starting-point—that is, that some antherozoids may not enter the egg until 
several hours after flooding. This, however, is rendered improbable by the 
uniformity in time of the first two or three phases. It is also possible, as is 
suggested by an exceptionally premature case of Phase 5 (Table I), that 
fertilization has sometimes taken place in the material studied before flood- 
