196 BARTHOLOMEW: Hyatopsora Po.ypopit 
lasting from three or four days to a week or more. During these 
periods the sori remained pale gray, but within twenty-four hours 
after the sun appeared they assumed a bright orange color. In 
contrast to this history, the sori that developed during the bright 
periods began to take on the yellow color even while they were 
quite small. Often a marked difference could also be noticed 
between the sori on shaded and on unshaded fronds—those on the 
former remaining gray for a considerable length of time, while the 
sori on the latter began to turn yellow almost as soon as they were 
noticeable. 
It is not difficult to dissect an infected pinna in such a manner 
that large masses of the mycelium may be obtained free from the 
host tissues. To do this most effectively, it was found best to 
soak the pinnae in Flemming’s weak fixing fluid for two or three 
Fic. Section through fixed and stained sorus, showing the peridium ( ods 
and stalked spores (ss), X about 390. Camera lucida drawing. 
hours, then to wash them in water for about the same length 
of time and afterward to dehydrate them by running them 
through a series of progressively stronger solutions of alcohol up 
to 95 per cent. A sorus was then cut from a pinna and dissected 
under a binocular microscope. Not only could mats of the 
mycelium be easily obtained in this manner, but in some cases 
rust spores remained attached to the hyphae. Often among the 
separated spores one was found with its short stalk still attached. 
This made it plain that the spores are not sessile as stated by Grove» 
but that, as Arthur says, they are borne on short stalks. This 
observation was verified by the study of sectioned and stained 
preparations (Fic, 1), 
