250 



HARDWICKE'S SCIENCE- GOSSIP. 



distinguish the threads and suspected spores from 

 the cellular tissue. I did not treat the leaves with 

 boiling water because I wished to keep the threads 

 and spores alive. 



From day to day I kept the diseased leaves, stems, 

 and tubers wet between pieces of very wet calico, in 

 plates uuder glass, and I immediately noticed that 

 the continued moisture greatly excited the growth 

 of the mycelial threads ; this to me was quite unex- 

 pected, as I had merely wished to set the spore-like 

 bodies free. So rapid was now the growth of this 

 mycelium, that after a week had elapsed, some 

 decayed parts of the lamina of the leaf were tra- 

 versed in every direction by the spawn. Thinking 

 the close observation of this mycelium in the now 

 thoroughly rotten and decomposed leaves might 

 end in some addition to our knowledge of Perono- 

 spora infestans, to which fungus I had no doubt 

 from the beginning that the threads belonged, I 

 kept it under close observation, aud in about ten 

 days the mycelium produced a tolerably abundant 

 crop, especially in the diseased tubers of the two- 

 sized bodies I had previously seen and measured 

 in the fresh leaves. The reason why these objects, 

 which undoubtedly occur in and about the spots, 

 are so extremely few iu number in those positions 

 is, I imagine, because they require a different set of 

 conditions for their normal growth, and these 

 conditions are found in abundant and continued 

 moisture. 



The larger of these bodies I am disposed to con- 

 sider the "oogonium" of the potato fungus, and 

 the smaller bodies I look upon as the " antheridia" 

 of the same fungus, which are often terminal in 

 position. The filaments of the latter are commonly 

 septate, and sometimes more or less moniliform or 

 necklace-like. Both oogonium and antheridium are 

 very similar in nature and size to those described as 

 belonging to Peronospora alsinearum and P. umbel- 

 liferarum ; and this is another reason (beyond my 

 seeing undoubted P. infestans on potato leaves at 

 the beginning of June) why I am disposed to look 

 upon these bodies as the oogonium and antheridium 

 of the potato fungus. 



The larger bodies are at first transparent, thin, 

 pale brown, furnished with a thick, dark, outer wall, 

 and filled with granules ; at length a number (usu- 

 ally three) of vacuities or nuclei appear. The 

 smaller bodies are darker in colour, and the external 

 coat is apparently marked with a few reticulations, 

 possibly owing to the collapse of the outer wall. I 

 have observed the two bodies in contact in several 

 instances. After fertilization has taken place, the 

 outer coat of the oospore enlarges, and soon gets 

 accidentally washed off in water. Both antheridium 

 and oogonium are so slightly articulated to the 

 threads on which they are borne that they are 

 detached by the slightest touch, but with a little care 

 it is not really difficult to see both bodies in situ; and 



my observations lead me to think that conjugation 

 frequently takes place after both organs are quite 

 free. The antheridia and oogonia are best seen 

 in the wettest and most thoroughly decomposed 

 portions of the tissue of the decomposing tuber, but 

 they occur also iu both the stem and leaf. I con- 

 sider Mr. Alexander Dean's remark, as reported in 

 the Gardeners' Chronicle for June 19th last, p. 795, 

 to have a distinct bearing on this point, where he 

 says, " In all cases where the seed tubers were cut 

 they were quite rotten." 



Before I referred to De Bary's measurements 

 of similar organs iu other species of Peronospora, I 

 was disappointed with the results of my observa- 

 tions, and felt disposed to refer the bodies and 

 threads in the potato leaves to Saprolegnia; but 

 a glance at the figures now published and the 

 similar figures copied from De Bary to the same 

 scale, will show that if the bodies observed by me 

 are Saprolegnia-like, the oogonia and antheridia 

 figured by De Bary show an exactly similar alliance. 

 Still, as the Saprolegniese are at present defined, 

 I am by no means inclined to describe the bodies 

 observed by me as really belonging to that tribe of 

 plants. 



The Saprolegnieae have the habit of moulds and 

 the fructification of algse, and they live on organic 

 matter, animal and vegetable, in a state of putre- 

 faction in water. One of the best known of these 

 plants is Botrytis Bassiana, the parasite which 

 causes the disease of silkworms. Now the genus 

 Botrytis among fungi is almost or quite the same 

 with Peronospora, to which the potato disease be- 

 longs ; and I consider it a strong argument in 

 favour of my Saprolegnia-like bodies being the 

 oogonia and antheridia of the Peronospora when 

 such an authority as Mr. Berkeley considers one of 

 the Saprolegniese (Achlya) " may be an aquatic form 

 of Botnjtis Bassiana" — the silkworm disease. 



The common fungus which attacks flies (so fre- 

 quently seen on our window-panes in autumn), 

 Sporendonema muscee, Fr., is said to be a terrestrial 

 condition of Saprolegnia ferax, Kutz., which latter 

 only grows iu water ; and if a fly infected with the 

 fungus be submerged, the growth of the Saprolegnia 

 is the result. It would now seem to be somewhat 

 the same with the potato when diseased, iu the 

 fact that when submerged a second form of fruit is 

 produced. 



Between the two moulds, Botrytis and Perono- 

 spora, there is little or no difference'; the characters 

 of Corda, founded upon the continuous or septate 

 filaments, caunot be relied upon, and even De Bary 

 himself figures P. infestans with septate filaments, 

 like a true Botrytis. The intimate connection, how- 

 ever, between the Saprolegniese aud some moulds 

 cannot be denied, as the instances above cited 

 clearly show ; and I am therefore disposed to think 

 that the fungus which produces the potato disease 



