296 
surface of the leaf, and the growth appears to be entirely 
arrested when this surface is in contact with the soil. It 
might be expected that under such circumstances the 
pustules would appear upon the exposed upper surface of 
the leaf as it hes upon the ground, but such is not the 
case ; the upper surface remains as free from the phoma as 
if the leaf did not contain the mycelium of it. Further in- 
vestigation may show that when this surface is continu- 
ously covered until the decay of the leaf, the fungus also 
dies without leaving spores for its future propagation ; but 
it has not yet been proven. The phoma makes a slow 
growth throughout the winter, and may be found as late 
in the following spring as May. When warm weather 
comes the black pustules begin the formation of another 
set of spores very different from the former kinds. These 
are quite large, oblong in shape, and contained in elongated 
sacs or asci; in short they are the ascospores of a mature 
form of an ascomycetous fungus. By the first of May the 
ascl or sacs are well developed, but the spores inside of 
them have barely become defined (Fig. 9), and some weeks 
droning longer are needed to develop and finally 
Ute i ¢(. bring them to a sufficient state of ripeness 
vedo '> for distribution, and a renewal of growth 
‘elcon.e”* when conditions become favorable. There 
Fig. 9.—Section are thus three sets of spores produced by 
showing theasci_ the fungus at different seasons of the year 
at the =e ee —the septoria spores insummer, the phoma 
form. Masnified SPOTeS In winter, and the ascospores in 
120 diameters. spring. 
Original. But at this point some critical reader 
may wish to inquire what reasons there are for believ- 
ing that these very different kinds of spores are really 
produced by the same fungus. There are several very 
ood ones. The resemblance which these successive 
orms bear to the course of development in other ascom- 
ycetous fungi, in which the life history has been well 
established, is strong presumptive evidence. To this is 
added the fact that the three stages overlap one another, 
that is, the phoma begins upon the same spots occupied by 
the septoria, and often before the latter has ceased produc- 
ing its spores, while the ascosporous condition in the same 
way follows the phoma, and this succession is invariable. 
A further point of evidence is that the phoma is in the 
same relative abundance as the septoria, and always follows 
it, while the same is apparently true of the ascosporous form 
in its relation to the phoma, although, from accidental 
causes, this has not been so fully observed. Until some 
proof can be adduced to the contrary, therefore, we shall 
be warranted in assuming’ that the three forms described 
are but developmental states of one fungus. 







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