306 Dey. — Studies in the Physiology of Parasitism. V. 
tube of B. cinerea into the bean-leaf was effected by a rupture of the cuticle, 
due to the mechanical pressure exerted by the germ-tube. 
The object of the present work was to make a careful microscopic 
examination of the stages of infection of the bean by Colletotrichum 
Lindemuthianum , and to discover if this fungus, belonging to a quite 
different group, acts in the same way as Botrytis cinerea. 
Methods . The cultures were made mostly in a medium of maize- 
meal agar, also on French bean-pods, autoclaved in test-tubes. The maize- 
meal agar medium was made in the following way — 30 grm. of maize-meal 
were cooked in 1,000 c.c. water at ioo° C. for half an hour. To this 
15 grm. of agar were added, and the mixture heated to no° C., to dissolve 
the agar. The medium thus prepared was ‘ tubed ’ and autoclaved at 
120 0 C. for 20 minutes. 
Spores were sown on slopes and Petri dishes. In three to four days 
small white patches appear. Examination of the young growth shows 
a felted mass of fine hyphae, with indications here and there of formation 
of acervuli. The hyphae frequently swell up into vesicles, as described 
by Stoneman (9), and branch copiously, giving a knotted appearance to the 
mycelium. After six days these spreading patches were dotted over with 
very small black areas, which even with a hand lens were seen to consist of 
very dark spines enclosing a pinkish spore mass. The spores are borne on 
short erect hyphae, which arise from swollen vesicles, and are abjointed from 
the tips of the hyphae, two or three in a series. At the same time mucilage 
is formed which surrounds the spores. After a few more days of growth 
acervuli become still more numerous, and gradually turn the white back- 
ground of mycelium into a black mass. The spore masses are now visible 
to the naked eye as round pinkish globules. The hyphae of the fungus 
are colourless, but the dark appearance of an old colony is due to the black 
stiff spines of the numerous acervuli. In cultures a month old or more, the 
spore masses, instead of remaining as moist pink globules, seem to dry up 
and shrink, becoming at the same time rather creamy in colour. They also 
become set with dark-coloured spines, so that old cultures become almost 
uniformly black and rugged in appearance. 
Germination of Spores. Spores from cultures about two weeks old 
were sown in thin films of sterile tap-water on a clean and flamed slide 
kept in a Petri dish containing sterile, moist blotting-paper. Under these 
conditions spores germinate quite readily in 18-24 hours at 20°-25° C. — 
the optimum temperature for the growth of the fungus, according to 
Edgerton (5), lying somewhere between 2i°-23° C. It was observed that 
if the drop of water containing the spores had a sharp convex surface, 
spores lying in the middle of the drop hardly germinated, while most of 
those lying near the border did ; this difference of behaviour is probably 
due to difference in oxygen supply. During the early stages of germina- 
