244 
W. B. Mercer, 
plasmolized and the cell walls will be rendered more distinct in conse¬ 
quence. It is less easy to induce the protoplasm to withdraw from the 
wall separating the two gametes Than from the other walls of these cells. 
This is especially true of the smaller gamete. It has been accomplished- 
in a sufficient number of cases, however, to leave no doubt in the 
writer’s mind that there are two gametes which are definitely separated 
by a continuous cross wall as shown in fig. 20. There seems no doubt 
also that these two gametes which plasmolize into two separate masses 
of protoplasm unite later by the dissolution of the intervening cross wall 
into a single cell the contents of which now plasmolize into a single mass 
as shown in fig. 23. 
Explanation of Plates. 
Figures in plates I and II were outlined with the aid of a camera lucida. 
half were all viewed through a 4 mm objective and have been reduced to about one 
They in reproduction. Surface sculpturing on mature zygospores is not represented. 
Plate I. Zygorhynchus heterogamus. 
Figures l—8. Consecutive stages in zygospore development in living material 
from moist chamber culture. Drawings were made at times indicated. 
Plate II. Zygorhynchus Aloelleri. 
Figures 9—15. Stages in zygospore development in living material from moist 
chamber culture. 
Figures 16—24. Stages of zygospore development taken from stained and mounted 
material. Outlines of cell walls only are represented, except in figures 20 and 23 
where plasmolized cell contents are shown in stippling, a Branch which has given rise 
to male gamete; b Branch which has given rise to female gamete; c Zygote formed by 
union of male and female gametes; m Male gamete; f Female gamete. 
On the Morphology and Development of 
Phoma Riehardiae n. sp. 
By 
W. B. Mercer, B. Sc. 
(Vans Dunlop Scholar, University of Edinburgh.) 
(With 6 Textfigures.) 
In a group of C^/Z^-plants under glass-house cultivation isolated 
leaves, partially or wholly in a state of decay, are usually to be found. 
Sometimes the decaying area is sharply marked off from the rest of the 
leaf; sometimes the transition from sound to unsound tissue is very 
gradual. The unsound area is usually situated peripherally; at times 
however it is represented by a round or oval area in the middle of the 
leaf, wholly surrounded by healthy tissue. In the examination of such 
unsound leaves, numerous fungi have been met with, notably species of 
Hormodendron , Alternaria , Macrosporium , Penicillmm etc. Together 
