OOPHYTA. 143 
to wires and strings hanging from the ceiling. The whitish powder 
around the fly will indicate the presence of the Fly-fungus. Mount 
some of this white powder in water and study under a high power 
to see spores. Examine some of the tissue of the fly (by tearing out 
small bits of the distended abdomen) for the internal portion of the 
parasite. 
(f) In the spring the leaves of shepherd’s purse and peppergrass 
may often be found covered underneath with a white mould-like 
growth (Peronospora parasitica). Carefully scrape off a little of this 
growth and mount first in alcohol, afterwards adding a little potassic 
hydrate. The irregularly branching hyphz will be seen to bear here 
and there their white, broadly ellipsoidal conidia. Similar studies 
may be made of the Grape-mildew (Peronospora viticola) on grape- 
leaves in autumn, and the Lettuce-mildew (Peronospora gangliformis) 
on cultivated and wild lettuce from spring to autumn. 
(g) Make very thin cross-sections of a leaf affected with a Mildew, 
when the latter has passed the period of its greatest vegetative ac- 
tivity. Mount in alcohol (to drive out air-bubbles), then add ‘potassic 
hydrate, and look for the resting spores, which in some species are 
of a dark-brown color. 
(hk) White Rusts occur on many plants: one (Cystopus candidus) 
on shepherd’s purse, peppergrass, radish, etc.; another (C. bliti) on 
amarantus; and another (C. portulace) on purslane. For conidia, 
make very thin cross-sections of leaves, through a white-rust spot, and 
mount as above. The resting spores (which are dark brown) are 
easily obtained in the leaves of amarantus and purslane. 
Cuass IV. Fucacnz (the Rockweeds). 
295. The plants of this class are entirely marine. In 
many cases the development of the plant-body is unusually 
perfect, showing a differentiation into parts which have a 
considerable resemblance to roots, stems, and leaves. In 
size they approach the flowering plants. Their tissues, too, 
show a high degree of differentiation; the cells are arranged 
in cell-masses, and these are differentiated into several va- 
rieties of parenchyma, approaching, in some instances, to 
the condition which prevails in the Mosses and their allies, 
296. With the foregoing there is found a marked differ- 
