Letters on the Diseases of JPlants. 



4n 



IX. Disease of the Onion. 



The flower cluster of the common onion is subject to the attacks of a disease 

 that, though not identical with the black-rot of the tomato, is, at any rate, 

 caused by a fungus nearly related to that causing black-rot — so similar that 



Fig. 57.— A disease found attacking tlie inflorescence 

 of the onion, a. Healthy flowers ; b, diseased and 

 dead flowers. This disease shows itself hy 

 hlackening and shrivelling the flowers so that 

 they do not set. The cause of the trouble is a 

 fungus similar in ai>pearance to that causing the 

 well-known black -rot of the tomato. The spores 

 of the fungus are shown in Fig. 58. There appears 

 to be two species here concerned, though but one 

 is abundant. 



Fig. 58.— Spores of the fungus 

 causing the onion disease 

 shown in Fig. 57. The two 

 upper left-hand spores are 

 of a second species. The 

 remainder appear to be 

 those of ClaAosponmn 

 herbanim. 



I have felt justiiied in recommending remedial measures of a nature similar 

 to those adopted for this latter disease. See Vol. V, p. 8SG. The nature of 

 the onion disease is set forth graphically in the illustrations. 



X. Timber Diseases. 



EvEET year brings me a number of inquiries as to the cause of the death of 

 the whole or parts of trees, generally fruit-trees, under peculiar circum- 

 stances, such as the absence of any apparent cause, or, at least, adequate 

 cause. Sometimes the deaths are sudden, sometimes not; but in most such 

 eases the disease has not been prolonged. These cases must not be con- 

 founded with death from lack of nourishment or care, or from old age. A 

 tree in good soil, and hitherto vigorous, suddenly sickens and dies, or perhaps 

 manages to hold out for a season or two and then dies ; such is the typical 

 case to which I refer. 



In such instances we at once suspect one of two causes, namely, insects 

 boring in the wood, or the presence of some timber-rotting fungus. 



In the former case the death of the tree or branch is often sudden. The 

 leaves wilt, dry up, and turn brown, as if a fire had scorched them, the whole 

 operation sometimes occupying only a few days. If a limb be cut away and 

 split up, the boring insects are usually disclosed. Their holes may also 

 usually be seen on the surface. (See Fig. 59, front tree.) 



