RICHARDS. — DEVELOPMENT OF ^CIDIA. 261 



leaves, owing to their comparatively loose structure, and to the fact 

 that the chlorophyll was mainly disorganized by the fungus, proved 

 the best for use. 



In the mature aecidium nothing of note is to be observed which 

 differs from the tecidium already described. The layers outside of 

 the hymenium are better developed and the peridial cells and spores 

 smaller than in the Kcidium on Peltandra. The whole ajcidium 

 is more compact. The intercalary cells are very prominent and in 

 them, perhaps on account of tlieir large size the double nuclei are 

 usually easily seen. 



The fertile hypha appears at about the same stage as noted before. 

 When it is traced back it is seen to merge into the rest of the 

 mycelium, and at first can only be told by its more granular and 

 refractive contents. Perhaps the best case observed was seen in 

 Figure 7, where at the base of a young primordium is seen a very 

 much twisted highly granular hypha which has already sent out a 

 branch from which the hymenium will develop, as in Figure 8. In 

 the somewhat older fecidia the young basidia may be seen to radiate 

 very distinctly from a common centre, which marks the position pre- 

 sumably of the end of the fertile hypha (Fig. 9). 



The subsequent development of the spores and peridium accords 

 well with that already described in the previous case, with the excep- 

 tion of the fact that the pseudo-parenchyma does not split as in the 

 aecidium on Peltandra, but is gradually pushed aside as the hymenium 

 develops. 



-^ciDiuM ON Ranunculus septentrionalis. 



On the lower sides of the leaves and on the petioles of Ranunculus 

 this species of secidium may be found occurring in clusters, with the 

 older fecidia in the centre and the younger around them. A con- 

 siderable quantity of the material was collected by myself in the 

 vicinity of Cambridge in the spring of 1894. 



The mature fecidia present no great peculiarities, with the excep- 

 tion of a very considerable variability in the size of the peridial cells. 

 Ordinarily they are large, much larger than the spores, but occasionally 

 specimens are found with very much smaller cells. In such cases, it is 

 quite easy to trace their connection with the spore chains below : they 

 differ but little from the spores in size, but have the characteristic 

 walls of peridial cells. It is possible that this condition may be 

 explained by a delay in the formation of the peridium in such cases. 

 The hymenium having attained its full size, there was not the same 



