70 FECUNDATION; NON-MOTILE ISOGAMETES. 
furnished by the male gamete. Chmielewskij (’90) finds that in all of 
the several species examined the chloroplast of the male gamete is 
dissolved in the zygote, that of the female only remaining. 
The behavior of the nuclei during fusion cannot be followed with 
any degree of certainty in the living specimen. As a rule they cannot 
be seen at all, a fact which led to the view of the earlier observers that 
the product of union was without a nucleus. One must, therefore, 
resort to thin and well-stained sections of properly fixed material to 
observe the details of nuclear fusion. For this purpose I have selected 
a small-celled species with one chlorophyll band. 
When the young zygote is provided with a thin cell-wall, the two 
nuclei, which are exactly alike, judging from their appearance, are 
seen lying closely applied to each other (Fig. 20, B). Each contains 
a rather large and distinct nucleolus and the characteristic linin net in 
which are imbedded small granules that behave toward stains as 
chromatin granules in resting nuclei of higher plants. In fact, the 
nuclei of SAzrogyra in this condition seem to possess the same 
structure as the phanerogamic nucleus. The contiguous parts of the 
nuclear membranes dissolve or disappear as such, and the network of 
the one unites directly with that of the other, the fusion of the nucleoli 
following later (Fig. 20,C). Frequently, before complete union of the 
nuclei, the wall of the zygospore may become much thickened and less 
easily penetrated by fixing fluids, so that perfect preparations are difficult 
to procure. During the development of the zygospore the chloroplasts 
become vacuolate and the identity of each cannot be made out. 
In the preceding paragraphs I have described the nuclear fusion in 
the zygote as I was able to follow it, but for lack of time and suitable 
material an exhaustive study of the subject was not made, and conse- 
quently I am not prepared to state whether the peculiar” behavior of 
the nuclei as described by Chmielewskij (’92) for Spzrogyra crassa 
and S. elongata is correct. Chmielewskij states that, as the gametes 
round up, the nuclear membranes become less distinct, disappearing 
entirely as the gametes unite. The nuclei now fuse, the fusion being 
complete by the time the zygote is provided with a thick, dark wall. 
This fusion takes place during the prophase of division. As soon as 
fusion is complete the nucleus divides. The daughter nuclei now 
divide, four nuclei resulting. Two of these then fuse, while the other 
two divide by direct division and finally disorganize. The fusing 
nuclei are provided with membranes and are in the resting condition. 
If the observations of Chmielewskij be true, the process in Spzrogyra 
is without parallel in the plant kingdom, at least so far as the author 
is aware. 
