﻿340 BOTANICAL GAZETTE [may 



especially at the time when asexual spores or conidia are formed, 

 during gametogenesis, and during the mitoses following the 

 fusion of sexual nuclei. Species of Albugo and Peronospora seem 

 to offer the best material for these investigations. Pythium, 

 although easy to cultivate and control, has nuclei so small that it 

 is almost impossible to study such details. The same diffi- 

 culties are met in the Mucorales and in part in the Saprolegniales, 

 and in the latter group the complications of apogamy render the 

 forms useless for these problems. Speculations on the reduc- 

 tion of chromosomes and the significance of various phases of 

 ontogeny in this group are almost futile until we have convincing 

 and complete data for one or more types. 



Whatever may be the significance of the mitoses in the game- 

 tangia, there is no proof that they are reducing divisions, and 

 it is probable that they are only phylogenetic reminiscences. 

 Stevens's observations that the nuclei in the second mitosis of 

 Albugo are much weaker in kinoplasm are interesting, but it is 

 very questionable whether such divisions are necessary steps in 

 the physiological differentiation of gametes. The mitosis may 

 have simply a phylogenetic relation and the lessened kinoplasmic 

 content be merely the result of that decrease in the size of the 

 nuclei characteristic of advanced periods of oogenesis in these 

 plants. 



Everything seems to point to the ooplasm as trophoplasmic 

 in character, first from the gathering of substance around the 

 coenocentrum and second from the effect of this structure on 

 nuclei in the vicinity. Staining reactions confirm this conclusion, 

 but it is not wise to lay too much stress on the effect of stains 

 in objects so small as these. And for this reason the judgment 

 that the gamete nuclei are weak in kinoplasm must be taken with 

 caution. The nuclei are generally smaller, and the conditions 

 are such that the majority of them must disorganize ; but the 

 reason for this run-down state must be chiefly the general nutri- 

 tive conditions of the gametangium, and not the mitoses of that 

 period. 



Stevens (1901, pp. 238, 239) lays stress on that period of 

 oogenesis in Albugo and Perenospora termed 'Ozonation," when 



