180 
POPULAR SCIENCE REVIEW. 
With a view to the clearer understanding of these parasites 
in the phases of their development, let us select one, and we 
cannot do better than adhere to that of the wheat and other 
graminaceous plants. A fine day in May or June dawns upon 
our preparations for a stroll, far enough into the country to 
find a wheat-field. Even now, with the area of the metropolis 
constantly widening, and banishing farmers and wheat-fields 
farther and farther from the sound of Bow-bells, a corn-field 
may be reached by a good stiff walk from Charing- Cross, or 
a sixpenny ride at the most, in nearly any direction. Having 
reached the field, it may be promised that a walk into it of less 
than twenty yards, will be sure to reward you with the fungus 
we are in quest of. Look down at the green leaves, especially 
the lower ones, and you will soon find one apparently grown 
rusty. The surface seems to be sprinkled with powdered red 
ochre, and grown sickly under the operation. Pluck it care- 
fully, and examine it with a pocket lens. Already the structure 
of a healthy leaf is familiar to you, but in the present instance 
the cuticle is traversed with numerous longitudinal cracks or 
fissures, within which, and about their margins, you discern 
an orange powder, to which the rusty appearance of the leaf 
is due. Further examination reveals also portions in which 
the cuticle is distended into yellowish elongated pustules, not 
yet ruptured, and which is an earlier stage of the same disease. 
This is the “ rust ” of the agriculturist, the Trichobasis rubigo 
vera of botanists, the first phase of the corn mildew. 
To know more of this parasite, we must have recourse to 
the microscope ; having therefore collected a few leaves for 
this purpose, we return homewards to follow up the investiga- 
tion. We will not stay to detail the processes of manipulation, 
since these will not offer any deviations from the ordinary 
modes of preparation and examination of delicate vegetable 
tissues. 
The vegetative system of the “ rust,” and similar fungi, 
consists of a number of delicate, simple, or branched threads, 
often intertwining and anastomosing, or uniting one to the 
other by means of lateral branchlets. These threads, termed 
the mycelium, penetrate the intercellular spaces, and insinuate 
themselves in a complete network amongst the cells of which 
the leaf, or other diseased portion of the plant, is composed. 
High powers of the microscope, and equally high powers of 
patience and perseverance, are necessary to make out this 
part of the structure. We may regard the whole mycelium of 
one pustule, or spore-spot, as the vegetative system of one 
fungal plant. At first this mycelium might have originated 
in a number of individuals, which afterwards became confluent 
and combined into one for the production of fruit, that is to 
