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its specific name, pygmaea. It has the pygmy conidiophores among the 
species of Plasmopara. Make a mount of Peronospora Ficariae from 
Ranunculus leaves provided, along with some of P. pygmaea in the same 
drop of water so that they can be compared as to size, form and branching. 
LOCATE :— 
11. A single entire conidiophore of each species well isolated in 
the mount. Study it carefully as to structure, thickness of walls, branching 
and arrangement of ultimate branchlets on which the conidia are borne. 
Make a large sKETCH of an entire conidiophore of each. Try to find in 
the mount a conidiophore with conidia still attached. Mounts from 
young leaves or the margins of lesions will often give conidiophores with 
conidia attached. If one cam be found, study a branch to determine the 
manner of attachment of the conidia. ; 
Study the mature conidia scattered through the mount. oBSERVE:— 
12. Their form; the slightly raised apical papilla to be dis- 
cerned on some of them; the thin wall and granular contents. pDRaw to 
show the form of the conidia of the two pathogenes. 
These conidia, produced in great abundance, are carried by the wind 
to healthy plants during rainy weather, initiating secondary cycles. 
Make an enlarged prawine of a section through a leaf of one of the 
hosts to show the pathogene-structures within and without the leaf. 
Saprogenesis. As the diseased tissue begins to die, the mycelium 
of the pathogene produces branches, the tips of which swell and round up 
between the cells to form oogonia and antheridia. Fertilization takes 
place and before the dead and fallen leaves begin to disintegrate, oospores 
are matured. 
(To study the sexual structures and development of the oospore, follow 
ble ew outlined under Downy Mildew of Grapes on p. 111, No. 20 
and 21. 
Oospores of Plasmopara pygmaea are produced in great abundance 
in leaf-lesions in Hepatica triloba as already observed under No. 6. To 
-understand the structure of the mature oospores and their relation to the 
tissues, examine prepared slides and make mounts from leaf-tissue mace- 
rated in potassium hydroxide. oBSERVE:— 
13. The numerous dark-brown bodies imbedded in the tissues. 
14. The oospore proper, with its uniformly thick smooth hyaline 
inner wall, and its outer brown wall, irregular in thickness; enclosing the 
oospore, the transparent thin old oogonial wall usually collapsed tightly 
against the outside of the oospore; remnants of empty hyphae. As these 
oospores are nearly mature, no trace of antheridia will probably be found. 
DRAW carefully to show the structure of a mature oospore, much en- 
larged. 
These oospores germinate in the spring as they lie in the old leaves on 
the ground, each giving rise to a conidiophore with conidia and so provide 
the primary inoculum as already seen. 
Secondary Cycles are initiated by the conidia produced during the 
primary cycle. Ordinarily, as in the case of the primary lesions, local 
lesions result. In the case of the secondary cycles initiated late in the 
season, the mycelium arising from the germtube may, instead of causing 
a local. lesion, spread throughout the stem and root of the plant without 
killing it. It becomes perennially associated with the tissues of the living 
host. It grows up into the new leaves put forth in the spring and sends 
