494 BOTANICAL GAZETTE [june 



again, the zygotes have the appearance of those formed by scalari- 

 form conjugation. This has been followed for 16 pairs of conjugat- 

 ing cells. In this case they are all in conjugation, and, strangely 

 enough, there are 8 zygotes in each filament. These filaments are 

 shown schematically in fig. i of pi. XXV, and in part in fig. i of 

 pi. XXIV. This is the only pair of filaments with any considerable 

 number of zygotes thus far found which shows the same number 

 in each of the conjugating filaments. A glance at the plates will 

 emphasize the fact that, in general, there is no such regular order. 

 Whole filaments would probably shed further light upon the occur- 

 rence. Moreover, filaments are found frequently in which both 

 true cross-conjugation and lateral conjugation occur. 



Much care is needed in the study of cross-conjugation, as there 

 are many chances for error. As previously stated, there are 

 combinations of scalariform and lateral conjugation that at first 

 appear to be cases of true cross-conjugation. The writer has used 

 the utmost care and has been compelled to discard a number of 

 slides that at first were thought to show cross-conjugation. Only 

 such cases as have complied with the following rules have been 

 regarded as in cross-conjugation: (i) zygotes must occur in 

 both filaments, the swelling of the egg cell is insufficient evi- 

 dence; (2) the connecting tube must be visible; (3) the male cell 

 must be empty; (4) end cells must be discarded unless the pre- 

 ceding conditions are met, since lateral conjugation may have 

 occurred. 



Slides have been permanently mounted in glycerine and from 

 these the microphotographs of pi. XXIV were taken. They are 

 made at 225 diameters. The plate shows the original photographs, 

 and no "retouching" has been done either on the plates or the prints. 

 Fig. 1 was made from a plain glycerine mount; while the others 

 were from slides stained either with iodine or Magdala red in order 

 that the cell walls might be made a little clearer. Figs. 2 and 6 

 show several filaments conjugating with each other. In the other 

 figures only 2 filaments are involved. These are, however, very 



clear 



cases. 



made (pi. XXV). In these 



filaments 





