130 REPORT OF THE COMMISSIONER OP AGRICULTURE. 



spots. TMs discoloration proceeded downward, until ultimately 

 many of the leaves appeared to be dead nearly to tlie base of the blade. 



Under a slight enlargement, the black points on old spots appeared 

 as velvety tufts of dark threads, protruding from the leaf. When 

 enlarged sufficiently to show the epidermal cells of the leaf, they were 

 seen to come from the stomata. As these occur in parallel lines, the 

 regular arrangement of the dots is explained by their occurrence over 

 the stomata. 



A section through a leaf in one of the discolored spots shows that 

 the epidermal cells are not much changed; but the parenchyma of the 

 leaf -pulp is much altered, its cells having lost their plump form, and" 

 being consequently more separated than in the healthy leaf, while 

 their normal green color has entirely disappeared, and yellow or 

 brown oil-drops are more or less abundant in them. 



These changes in the leaf are shown by such a section to be con- 

 nected with the presence of a colorless mycelium of branched, occa- 

 sionally septate threads running TDetween the pulp-cells. Under the 

 stomata the mycelium collects in a more compact form, as a sort of 

 false parenchyma, the upper cells of which assume a smoky-brown 

 color, and ultimately emerge through the stomata as a tuft of slightly 

 wavy, more or less knotty, dark hyphse, constituting the dark points 

 that have been already referred to. When these tufts are small they 

 merely crowd the stomata open to their fullest capacity, but in most 

 cases they enlarge so as to tear the ejjidermis open. 



The hyphte which have emerged into the light in this way produce, 

 as a rule, a single smoky -brown conidial spore each, which is borne 

 at the apex. Occasionally a spore is also found at one of the knots 

 along the side of a hyplia. The spores originate as enlargements of 

 the contracted tips of the hyphEe, and at first are globular, then 

 obovid, and finally somewhat spindle-shaped. When partly grown 

 they are separated from the ends of the hyphse by thin walls, which 

 split across when they are ripe, allowing them to fall. The center 

 of each tuft of hyphse is the oldest, and sheds its spores first. As the 

 tuft enlarges new hyphas are crowded through at its margin, so that, 

 forming spores, others which are ripe and old hyphse that have shed 

 their spores, may be seen in a single section, as in Fig. 2. When 

 fully mature the spores are typically two-celled, by a partition at or 

 below the middle; but many of those which fall from these stalks 

 and are apparently ripe are only one-celled. 



The disease is jiropagated by these bodies, which germinate by 

 emitting slender, flexuous. or contorted colorless mycelial threads 

 (Fig. 2 A. ) These make their way through the stomata of the grass 

 leaf and develop between the leaf cells, forming the mycelium that is 

 "seen in section of diseased leaves, which nourishes itself at the exj)ense 

 of the cells it grows between, and which are ultimately destroyed. 



The appearance of many of the older diseased leaves suggested that 

 the fungus may have first attacked the dead tips of the short leaves 

 parched by the drought. That it also causes the disease of otherwise 

 fresh and healthy leaves is shown by the occurrence of the charac- 

 teristic dark spots, bearing tufts of fertile hyphee on green parts of 

 these leaves, and on younger leaves that were only partly developed 

 and entirely uninjured, except for the fungus. 



The parasite which caused this spot disease of orchard-grass is 

 Scolecotriclium graniinis, a sjiecies Avhich occurs on various grasses 

 in Europe, and has been collected once or twice in this country. It 

 is one of the so-called imperfect fungi, and may be only a form of 



