The Besting Scores of the Potato Fmigus. By W, O, Smith, 119 
especially in the very putrid stems and in the tubers when in the 
last stage of decomposition. Mr. Berkeley afterwards found them 
with abundant mycelium, after the meeting of the Eoyal Horticul- 
tural Society on July 7, where he exhibited a drawing of one resting 
spore still attached to its thread. Mr. Broome (from material sent 
by me) has also detected and sketched, together with the immature 
sphserical bodies, one of these brown, coarsely-marked resting 
spores, but it was so involved in the mycelial threads (so he writes 
me) that he could not set it free. It is quite possible that the 
condition of the Potato, as seen during the present season, is quite 
exceptional, and that it may not occur again for a long series of 
years. Mr. Broome has written me to say he has never seen any- 
thing similar in diseased Potatoes. 
In the accompanying illustration, which is an exact copy of the 
first sketch taken, the oogonia and antheridia are seen in the sub- 
stance of the lamina of the leaf, the two bodies being in contact at 
H, J. In Fig. 5, PL CX V., many more of the same bodies are shown ; 
some in actual contact ; the two upper figures, K and L, show the 
resting spores some time after fertilization, when a coat of cellulose 
is the result. In K the spore is surrounded by this coat, whilst at 
L the spore is accidentally washed out by maceration in water. 
The semi-mature resting spores, as shown in these figures at M M, 
are furnished with a dark coat or skin; this coat, when further 
maturity is reached, clearly resolves itself into two layers, the 
inner one being termed the endospore, and the outer, which in 
PeroTWspora infestans is almost black in colour and warted, the 
exospore. The latter resembles in outward aspect, instead of one 
spore, a dense concreted mass of minute brown-black bodies. The an- 
theridia are shown at N N. The perfected resting spores are slightly 
egg-shaped, and on an average are one-thousandth of an inch in 
diameter. The oosphere is fertilized by the contact of the anthe- 
ridium ; when the two bodies accidentally touch the latter fixes a . 
small branch or tube, called a poUinodium or fecundating tube, 
into the wall of the oogonium, and discharges part of its contents 
into the protoplasm of the infant resting spore ; when these resting 
spores are mature the mycelial threads soon vanish, and the spores 
are free. 
When I read my first notes before the Koyal Horticultural 
Society I had not been able to detect this fecundating tube, but 
since then I have several times seen it. After the Potato plant 
has been badly attacked and destroyed by the fungus, every part of 
the plant and its parasite perishes, except the dark-brown warted 
resting spores just described, and these find their way into the earth 
and hibernate. When they awake to renewed life in the summer 
they must germinate in the damp earth, and if no Potato plants 
are near they perish, as the earth cannot support them ; in this 
VOL. XIV. K 
