THE WHITE RUST, ETC. 473 
to eight days their germination might be observed when 
placed in a drop of water. This method again corresponds 
with the ordinary processes by which the plant naturally 
decays on exposure to the influences of the atmosphere, and the 
oospores germinate under the favour of a shower of rain. 
If the oospore, after the decay of the tissues, is isolated and 
placed in a drop of water, the brown investing membrane will 
be seen to rupture irregularly, and its contents (enclosed in a 
transparent inner membrane) issuing from the orifice. As in the 
case of the conidia, this body at first contains vacuoles, and is 
afterwards divided into polyhedric portions ; these pass into 
zoospores which congregate at the centre into a globular mass. 
They afterwards separate, and for some minutes float about 
in the vesicle in which they were generated. Ultimately the 
membrane ruptures, and the zoospores swim about in the 
water just as those produced from the conidia had done. The 
number contained in each oospore is considerable, and may 
be estimated at not less than one hundred. 
The zoospores, whether produced from conidia or from 
oospores, appear to be the same. The movements of both in 
the water last from two to three hours ; then they cease, the 
cilise disappear, and the zoospores remain at rest, taking 
meanwhile a globular form. Afterwards these spores (for 
having ceased all motion they are no longer zoospores) emit 
a thin tube from some portion of their surface, such tube 
attaining a length of from two to ten times that of the spore 
whence it proceeds. The extremity of this tubes swells and 
forms a kind of cell into which the contents of the spore pass 
through the medium of the tube. 
Thus far, and thus far only, has Dr. de Bary been enabled 
to trace the development of the zoospores in a drop of water. 
Another series of experiments was instituted by this mycolo- 
gist having especial reference to the parasitism of the “white 
rust.” He made numerous observations to ascertain whether 
the spores of the germinating tubes entered by the roots of 
growing plants, and satisfied himself that they did not. 
Plants of g’arden-cress, mustard, and shepherd's-purse had their 
roots immersed in water impregnated with zoospores. After 
one or two days, though the surfaces of the roots were covered 
with zoospores that had emitted their germinating tubes in all 
directions, none had penetrated or showed the least tendency 
to penetrate the epidermis. Other plants were planted in 
flowerpots and watered at the roots with water charged with 
zoospores, and for two days the pots were left standing in the 
water similarly charged, then the plants were removed, culti- 
vated in the ordinary manner, grew up healthy, and gave no 
signs of the white rust. Care had been taken that neither 
