April i, 1884.] 



THE TROPICAL AGRICULTURIST. 



7>S 



remark is pertinently made that bad weather is an accid- 

 ental circumstance, the influence of which is proved to 

 be unlikely by the regularity with which the diminution 

 of yield has progressed of late years. 



The facts quoted by M. Brunat, as to the silkworm 

 disease in Europe, are of value in appreciating the situ- 

 ation of matters in Ohiua, as depicted by his further ex- 

 planations. In 1863, the annual jrield of silk in France 

 was 40,(KH3 bales, but the etfects of a malady similar to 

 that now existing in China gradually reduced the pro- 

 duction, until a miuinniui annual (juantity of '.i,(MJO bales 

 was arrived at. At first, it was thought that the disease 

 was in the mulberry leaf, but subsetiuent investigations 

 establislied the fact that the malady was hereditary in 

 the silkworms tliemselves. It was attempted to import 

 seed from lands where the disease had not yet ap- 

 "peared, but all the producing countries were gradually 

 attacked, and although in Ohiua the disease only existed 

 in a latent form, it manifested itself clearly in such 

 Chinese seed as was imported into Europe. 



During the period from 1865 to 1870, M. I'asteur was 

 engaged (at the instance of the French Government) in 

 carefully studying the causes of the disease, and in devis- 

 ing means of curing, or at least preventing it. His in- 

 vestigations allowed him to report to the following effect; — 

 1. That the most destructive malady was pfbrine, or 

 disease of the corpuscles, which had causeil the ravages 

 of previous years. 2. That this disease is hereditary and 

 contagious, and that it is developed by want of care 

 in the rearing of the silkworms, kc. 3. That the distinct- 

 ive character of this disease is the presence in the body 

 of the diseased subject of small corpuscles, which can 

 be sir:i wiiU a microscope, and which increase in number 

 as the malady develops itself. Further, that microscopic 

 observation should be made use of in the selection of 

 seeds or eggs for preservation. 



This malady is compared with consumption in the 

 human subject. 



It is remarked that M. Pastenr's theories were at first 

 mot at times by disbelief, but it is upon the principles 

 thus laid dowu that the measures were subsequently 

 taken, winch have resulted in the French and Italian 

 yield of silk having recovered a good deal of the import- 

 ance of former times. In addition to pi'hrine, there is 

 a disease named jlacherie. which effects the intestinal canal 

 of the silkworm, and which has also to be combated ir 

 China. — JournaX of the Society of Arts, 



GUMMING IN FRUIT TREES. 



An essay, by my friend Dr. Beijerinck,* on the con- 

 tagion of the gum-disease in plants, which has lately been 

 published by the Royal Academy of Sciences at Amster- 

 dam, contains so many facts likely to be useful in the 

 study of cont-agion that I venture to ask you to insert a 

 brief notice of its chief contents. The gum disease (gum- 

 mosis, gum-flux) is only two well known to all who grow 

 Peaches, Apricots, Plums, Cherries, or other stone fruits. 

 A similar disease produces gura-arabic, gum-tragacanth, and 

 probably many resins and gum-resins. It shows itself openly 

 ia the exudation of thick and sticky or hard and dry lumps 

 of gum, which cling on branches of any of these trees 

 where they have been cracked or wounded through the 

 bark. To any students of medicine or pathology who live 

 within range of such trees, Dr. Beijerinck's observations 

 may suggest some interesting researches. 



Dr. Beijerinck was induced to make experimental in- 

 oculations of the gum-disease by suspicions that, like some 

 others observed in plants, it was due to bacteria. He as- 

 certained that it is in a high degree contagious, and can 

 easily be produced by inserting the gum under the edge 

 of a wound through the bark of any of the trees above- 

 named. The observation that heated or long-boiled pieces 

 of gum lose their contagious property made it most prob- 

 able that a living organism was concerned in the con- 

 tagions; and he then found that only those pieces of the 

 gum conveyed contagion in which, whether with or with- 

 out bacteria, there were spores of a relatively highly or- 

 -anised fungus, belonging to the class of ascomycetes ; 



* Onderzne kimjen over tlr ne^mfiteU jkhcid dcrOom-icl'tehj: 

 riaitten: door Dr. M. W, Bi-iiennck. Amsterdam, 1S83, 4to 



and that these spores, inserted by themselves under the 

 bark, produced the same pathological changes as did the 

 pieces of gum. 



The fungus thus detected was examined by Professor 

 Gudemans, who ascertained it to be a new species of Cory- 

 neum, and has named it Ooryneum Beijerinckii. Its char- 

 acters, which are minutely described, are chiefly that it has 

 a cushion-like stroma, consisting of a bright brown paren- 

 chyma, on which numerous conidia stand on colourless, 

 unicellular and very slender stems, about as long as them- 

 selves. The conidia are small, cask-shaped, about one- 

 thirtieth of a millimetre in length, and usually divided by 

 slightly constricting septa into four cells, of which the 

 two terminal are longer than the two middle. From these 

 cells germinal filaments may proceed, from which are de- 

 veloped either yeast-cells, or brown thick-walled and many- 

 celled mycelia. 



The inoculation experiments aro best made by means of 

 incisions through the bark of young branches of healthy 

 peach trees or Cherry trees, and by slightly raising the 

 put edge of the bark and putting under it little bits of 

 gum from a diseased tree of tht^ same kind. In nearly 

 every instance these wounds become the seats of acute 

 gum disease, while similar wounds in the same or other 

 branches of the same tree, into whic^ no gum is inserted, 

 temain healthy, unless, by chance, gum be washed into 

 them during rain. The inoculation falls only when the 

 inserted pieces of gum contain no Ooryneum. 

 i By similar inoculations similar diseases can be produced 

 in Plum, Almond, and Apricot trees, and with the gimi 

 bf any one of these trees any other can be infected ; but 

 of many other substances which Beijerinck tried, not one 

 produced any similar disease. 



■ The inoculation with the gum is commonly followed by 

 the death of more or less of the adjacent structures; first 

 of the bark, then of the wood. 8mall l>ranches or leaf- 

 stalks thus affected in winter, or in many places at the 

 same time, may be completely killed; but in the more in- 

 structive experiments the first symptom of the gum-disease 

 Is the appearance of a beautiful red colour around the 

 Wound. It comes out in spots like those which often ap- 

 pear spontaneously on the green young branches of Peach 

 trees that have gum-disease ; and in these spots it is usual 

 to find Ooryreum-stromata, or mycelium-filaments. The 

 colour is due to the formation of a red pigment in one 

 or more of the layers of the cells of the bark. 



But in its further progress the disease extends beyond 

 the parts at which the Lloryneum, or any structures de- 

 rived from it, can be found; and this extension, Beijerinck 

 believes, is due to the production of a fluid, of the nature 

 of a ferment, produced by the Ooryneum. and penetrating 

 the adjacent structures. This, acting on the cell-walls, 

 the starch-granules, and other constituents of the cells, 

 transforms them into gum, and oven changes into gum the 

 Ooryneum itself, reminding the observer of the self-digeston 

 of a stomach. 



In the cells of the cambium, the same fluid penetrating 

 unites with the protoplasm, and so alters it that the cells 

 produced from it form, not good normal wood, but a mor- 

 bid ])arenchymatou6 structure. The cells of this paren- 

 chyma, well known among the features of gum-disease, are 

 cubical or polyhedral, thin-walled, and rich in protoplasm. 

 This, in its turn, is transformed into gum. such as fills 

 the gum-channels and other cavities found in wood, and 

 sometimes regarded as gum-glands. And from this also the 

 new ferment-fluid constantly produced, and tracking along 

 the tissues of the branches, conveys the Coryneum infec- 

 tion beyond the places in which its mycelium can be found. 

 — Communicated by Sir James Paoet, Bart., F.K.S. — Gard- 

 eners^ Chronicle. 



ST. HELENA. 



Mr. D. Morris, the Director of Public Gardens and Plant- 

 ations in Jamaica, has written a Report npon the I'rrsent 

 I'o^'ition (ind Prospects of the Ar/ricif/tiiral Iiesonrres ff the 

 Island of St. Helena, wliich has just been printed by the 

 Colonial Office, and which contains much matter of inter- 

 est, as our readers may infer from the short account wn 

 are now able to give. 



St. Helena has an historical interest to every English- 

 man, in consp((ueuce of its being the island home of the 



