3i4 
Wager . — On the Structure and 
to judge of the length of time which these stains should be 
allowed to act, but I have found that the best results are 
obtained by a very short stay in carmine. I have occasionally 
found it useful to differentiate in Hydrochloric acid alcohol. 
The sections are then transferred to 70 °/ o spirit, methylated 
spirit and absolute alcohol. They are next transferred to 
xylol or carbolized xylol and mounted in xylol balsam. 
I have used in the investigations the apochromatic lenses 
of Zeiss ; 4-0 mm., apert. 0-95 ; 2*0 mm., apert. 1*40, and oculars 
8, 12, and 18. In order to obtain the best illumination possible, 
I used a high-angled oil-immersion condenser, and recently 
the Welsbach Incandescent light, which surpasses anything 
I have previously worked with. 
Structure of Mycelium and Haustoria. 
The mycelium is not so easily seen, and its structure is 
more difficult to observe than is the case in Peronospora 
parasitica , which commonly occurs with Cystopus on the 
same host-plant, and it may be easily overlooked unless it is 
present in abundance. The hyphae are irregular in size and 
outline, according to the shape of the intercellular spaces 
through which they pass, and branch frequently. The 
branching is very irregular, depending upon the presence of 
the intercellular spaces, and it occasionally happens that 
when a branch reaches a larger intercellular space than usual 
it expands considerably and produces branches radiating 
from it in all directions. The protoplasm contained in the 
hyphae is granular, and loosely arranged in a network with 
numerous meshes. It is sometimes very scanty in amount, 
and forms just a thin layer on the wall of the hypha with 
a few strands stretching across here and there. It is on the 
other hand occasionally very dense indeed, completely filling 
the lumen of the hypha. This occurs where probably active 
growth is taking place, and is often found in those portions of 
the mycelium on which the basidia are borne. In the normal 
condition the protoplasm stains reddish blue in the carmine- 
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