6 BROOKLYN BOTANIC GARDEN MEMOIRS 



of the young zygote is symmetrical in relation to the two gametangia, 

 that is, the tip of each gametange shares equally in the growth. In 

 other cases the new growth arises more from one than the other, 

 usually from the larger one where they are unequal in size. More 

 rarely does the new growth arise entirely from the larger gametange, 

 but the communication is so broad that both gametangia remain in 

 direct communication with the contents of the new growth. This new 

 growth, or progressive zygote, enlarges to a broadly elliptical structure, 

 35-60 X 30-45 )U. It stands on the two supporting gametangia, and 

 the protoplasm of the gametangia and new zygote is continuous. 

 When the new zygote has reached its full size the protoplasm in the 

 gametangia withdraws and merges with that in the zygote. A new 

 wall is now laid down inside of the primary zygote membrane. At 

 first thin, it increases in thickness, forming a white, stratified, carti- 

 laginous layer around the protoplasm, thus cutting off communication 

 with the empty gametangia. The two stalks which support the mature 

 resting zygote are not simply the suspensors, but the empty game- 

 tangia plus the suspensors. The resting zygote is nearly filled with 

 very minute rounded or slightly irregular hyaline bodies, which appear 

 to be fat bodies, since they stain red with Sudan III. There is a 

 rounded clear space in the center, i. e., in the middle of the long axis, 

 but in some zygotes it lies on one side next the wall. In fixed and 

 stained material the center of this vacuole (?) appears to be occupied 

 with a coarsely granular body or mass of minute bodies. 



Cytology of conjugation and zygote formation. — ^The number of 

 nuclei in the gametangia is variable, probably from five to ten or more 

 in each. No evidence of nuclear division in the progametes or game- 

 tangia has been observed, and no evidence has been seen of a selection 

 of gamete nuclei. Nor does it appear that there is any nuclear de- 

 generation in the progametes before the formation in the cross wall 

 which differentiates the gametangia. Following this stage nuclei in 

 the suspensors may degenerate. The cytoplasm in the gametangia 

 is so dense and stains so deeply that it is sometimes difficult to differ- 

 entiate the nuclei. When the stain is not too deep the nuclei are 

 clearly seen. They are considerably larger than the vegetative nuclei, 

 the increase being due to growth. There is a nuclear membrane, a 

 clear court in which are sometimes visible a few delicate threads, per- 

 haps portions of the linen or chromatin. There is a prominent central, 

 spherical, nucleolus or karyosome, which stains red with Flemming's 

 triple stain, dark with iron haematoxylon. The nuclei are disposed 

 in the cytoplasm of the gametangia without order. They gradually 

 migrate into the new zygote, as it is formed, along with the cytoplasm. 



In the young zygote the cytoplasm is at first dense and rather 



