93 
ting and in other ways to the neighborhood of healthy plants and so 
initiate secondary cycles. 
Saprogenesis. The evidence seems to show that this pathogene 
may vegetate as mycelium in old host-debris and often in the soil. At 
least it develops on dead plant-parts and many strains appear to be almost 
obligate saprophytes. 
A sexual form of the pathogene, the Corticium stage, is at times de- 
veloped, and always on the surface of the living plant-parts above the 
ground, i.e. on stems and leaves. Apparently it does not always occur in 
the life-cycle. It may appear on the healthy parts above a Rhizoctonia 
lesion or on the stems and leaves of plants which show no such lesions or 
other evidences of injury. There is no indication that the fungus is ever 
pathogenic in this stage. 
Examine the material provided, OBSERVE :— 
32. The thin, white, weft-like coating over the surface, very 
difficult to discern in dried or pressed material. 
Scrape and mount some of this coating; examine under the micro- 
scope and OBSERVE :-— 
33. That it is made up of a much-branched and septate mycelium. 
How does it compare with the vegetative mycelium of the Rhizoctonia 
stage as to size, branching and septation? 
34. The swollen tips of many of the branches each bearing two 
to four pointed sterigmata. These are the basidia. 
35. Scattered through the mount, the small, hyaline, ovate 
basidiospores. Some half-formed or nearly matured spores still attached 
to the sterigmata may sometimes be found. 
Make a DRAWING of the mycelium of the sexual stage, showing the fruit- 
ing structures or copy from Colorado Bul. 91, pl. III. 
The mycelium of the sexual stage appears to develop from the sclerotia 
on the underground parts of the host, or from the mycelium in the dead 
tissue of lesions, or from host-debris in the soil. It spreads upward over 
the surface of the living parts, without causing any direct injury, to a 
position where spores may be formed and readily disseminated. 
The basidiospores are scattered by the wind. It is almost certain that 
they never function in directly infecting a healthy plant but germinate 
and develop a saprophytic mycelium which may go into the sclerotial 
stage or at once attack healthy plants. 
The development of a considerable amount of saprophytically nourished 
mycelium in and about the infection-court seems to be a necessary prelude 
to an attack on living tissue. 
Secondary Cycles are frequently initiated during the growing-season 
by spreading or broken-off, vegetative mycelium. Sclerotia are readily 
formed and their barrel-like cells germinate at any time when conditions 
favor, so that they are doubtless a frequent source of secondary inoculum. 
So far as known, secondary cycles duplicate the primary in all details. 
REPORT 
1. Enumerate the facts in regard to the morphological structures 
and life-habits of C. vagum B. & C. which make its control difficult and 
explain why in each case. i: ; 
2. Outline a plan for reducing the ravages of this disease in one 
of the crops which it affects. 
