254 



HARDWICKE'S SCIENCE-GOSSIP. 



itself, so tbe resting spores of the potato fungus 

 have without doubt been found this year in the 

 potato plant. 



How this came about is now pretty generally 

 known. Mr. Murray exhibited some specimens of 

 potato leaves badly diseased, before the Scientific 

 Committee of the Royal Horticultural Society. In 

 the corroded spots of these leaves Mr. Berkeley's 

 sharp eye detected dark-brown warted bodies (but 

 no mycelium), which he referred to the genus 

 Protomyces. Assuming these bodies to be the true 

 resting spores, which they doubtlessly are, they 

 were necessarily free, as the coat of cellulose dis- 

 engages tbem from the mycelial threads. But some 

 similarly spotted leaves had been previously sent on 

 to me from the Journal of Horticulture, upon which 

 I detected the old potato fungus, mycelial threads 

 within the leaves, and some circular transparent 

 bodies of two sizes, new to me. 



In attempting to wash the circular bodies out of 

 the leaves and stems, by maceration in water, I 

 found the moisture greatly accelerated the growth 

 of the mycelium, and that the long-sought-for 

 cm .gonium and antheridium were at length the result. 

 These bodies were at first most sparingly produced, 

 so that for many days, and after most careful 

 searching, I could only find one or two. After- 

 wards I found them more abundantly in different 

 stages of maturity, 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 Royal Horticultural 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 spherical 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 anything similar in diseased potatoes. 



In the preceding illustration, which is an exact 

 copy of the first sketch taken, the oogonia and 

 antheridia are seen in the substance of the lamina 

 of the leaf, the two bodies being in contact at H J. 

 In fig. 163 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 macera- 

 tion 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 ma- 

 turity is reached, clearly resolves itself into two 



layers, the inner one being termed the endospore, 

 and the outer, which in Peronospora 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 antheridia 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 oospuere is fertilized by 

 the contact of the antheridium ; when the two 

 bodies accidentally touch, the latter fixes a small 

 branch or tube, called a pollinodium 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 Royal 

 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 de- 

 scribed, 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 they are not 

 unlike the seeds of germinating Dodder ; for if they 

 cannot find a proper host they die. But if potato 

 plants happen to be near the corrosive mycelium, it 

 at once penetrates and enters the tuber or haulm. 

 The tuber cannot produce simple or zoospores if 

 buried, but in the haulms the mycelium doubtless 

 soon grows and produces both these forms of fruit. 

 These are at once carried by the air into the 

 breathing pores, and the whole history of the fungus 

 here described is re-enacted. 



Since my observations on these bodies were 

 published in the Gardeners' Chronicle for July 10, 

 I have (by the courtesy of the Rev. M. J. Berkeley) 

 had an opportunity of carefully examining and 

 measuring the original specimens of Dr. Montague's 

 artotrogus, found long ago in the intercellular pas- 

 sages of spent potatoes, and from the first considered 

 to be the secondary form of fruit of the Perono- 

 spora by Mr. Berkeley. I have no hesitation 

 whatever in saying that the bodies lately seen, and 

 now figured by me are positively the same with 

 Dr. Montagne's in every respect, and when reflected 

 and traced with the aid of a camera lucida no dif- 

 ference whatever can be detected. The bodies seen 

 in Dr. Montagne's specimens are, without doubt, 

 the fertilized and half-mature resting spores, and 

 therefore dense, uncollapsed, and exactly the same 

 in size, habit, aud colour with mine when in the 

 same stage of growth. After the lapse of so many- 

 years the threads, as might be expected, have more 



