Cytology of Pythium ultimum , n. sp. 303 
To which of these two cases does our plant belong? If 
a second division occurs in the gametangia, accompanied by a 
reduction in the number of chromosomes, then it obviously 
belongs to the first. If no second division takes place, it 
does not necessarily belong to the second. There may be a 
third type, with the features of which we are not yet acquainted. 
It would have, of necessity , to go into the second group only if 
it could be shown that a process of reduction in the number of 
chromosomes takes place in the germinating or resting zygote, 
similar to that which is supposed to take place in the embryo- 
sac mother-cell of Lilium. 
We can, unfortunately, come to no definite conclusion from 
the facts hitherto disclosed in this species. The probabilities 
are that the gametes have nuclei with the same number of 
chromosomes as those of the vegetative nuclei. We are thus 
brought face to face with the fact that an apparently unneces- 
sary nuclear division takes place. What is the significance of 
this division ? The view advanced first by Hartog in a similar 
case and provisionally adopted by others, that it is an ancestral 
character with no present physiological significance, does not 
appeal to me if only for the reason that it tends to check further 
investigation. Moreover, its general occurrence in coenocytic 
plants of widely different character, such as Cystopus Bliti , 
Peronospora , Saprolegnia , Achlya , and Pythium , suggests that 
its present importance is by no means inconsiderable. The 
case of Pythium suggests the validity of the explanation 
which has already been advanced by Strasburger (’97), that 
these divisions are essential stages in the differentiation of 
gametes. As a general view the theory, however, does not 
appear to be admissible, for, according to Lagerheim (’00) 
and Oltmanns (’95) there do not appear to be any preliminary 
divisions in M onoblepharis and V aucheria. In the Perono- 
sporaceae and Saprolegniaceae the case is different. In 
Pythium in particular the unpractised eye cannot distinguish 
a conidium from a young oogonium. It is demonstrable too, 
in sections, that by the time the young antheridium makes 
its appearance the oogonlal nuclei are preparing to divide. 
