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♦ KNOWLEDGE ♦ 



[Adg. 29, 1884. 



preside over the disintegrating processes of decay and putre- 

 faction. Their spores abound in the air of towns, and in 

 rural places that are not very high above the sea level and 

 remote from sources of contamination. Their adaptation 

 to various conditions of heat, cold, moisture, dryness, rich 

 or poor supply of appropriate food, <feo., is obtained by their 

 power of modifying their growth according to circumstances 

 to an extent quite unknown amongst the higher plants. In 



the group of objects in the sketch some are spores of 

 different shapes, some naked, some in little bags (asci). The 

 tubular threads are the mycelium which produces them. 

 There are also numbers of extremely minute round objects, 

 which are no doubt capable of starting fresh growths. A 

 fungus spore may be a single cell growing out of a spicular 

 or a thread-like support ; or it may be produced in an 

 cscus, or sporange (spore vessel), or be in a dust-like condi- 

 tion, conidia (secondary spores). 



What is a spore 1 This question requires a rather elabo- 

 rate answer, and, in reply, it is perhaps best to explain 

 what seed is in the higher plants. In the phanerogams, or 

 plants which show distinct sexual organs, pollen-bearing 

 anthers, pistils, and ovaries, the seed is the result of pollen 

 action upon a plant egg, or ovule. This seed produces a 

 plant like the parent by apparently direct growth. If we 

 look to the spore of one of the higher vascular cryptogams 

 — say a fern — its first visible process of development is a 

 little expansion called a pi-othaUiuyn, and then comes the 

 growth of sexual organs, and their concurrence to give 

 rise to a new plant. Vegetable physiologists trace resem- 

 blance between pollen grains and spores, and Sichs tells 

 us that " the fertilised embryonic vesicle of phanerogams 

 is not directly developed into the embryo ; it first 

 of all produces a pro-embryo, the suspensor growing 

 towards the base of the embryosac, and dividing, and on 

 the apex of which arises a mass of tissues from which the 

 embryo is developed." To a beginner this will seem rather 

 obscure, but what it means is this : that the plan of nature 

 is similar and continuous from lower to higher forms, and 

 there is no impassable gap between the growth of a spot of 

 mould upon stale paste and the reproduction of an oak from 

 an acorn its parents made. Besides spores which are 

 adapted to immediate development, fungi produces resting 

 spores, which can wait uninjured for another season, and 

 the dust-like conidia are, in many cases at least, able to 

 withstand prolonged drought. " The same species," observes 

 Berkeley, " may at different times have simple, uniseptate, 

 or multiseptate fruit, and its form will vary in different 

 asci of the same individual, though some general characters 

 may be exhibited by all." 



To determine the species of a fungus accurately, it is 

 necessary to know it in all its forms, which, in a great 



many cases, no one has succeeded in doing, and the number 

 of real species is probably only a fraction of those men- 

 tioned in the books. The modes of reproduction of fungi 

 are very various, but Sachs informs us that in those species 

 whose cycle of development is fully known, either sexual 

 reproduction, or conjugation — a form of it — always occurs, 

 and in those cases where neither of these processes has 

 been observed, it may be assumed that their life history is 

 incomplete. 



The black fungi which more immediately concern us, 

 are often terribly destructive when they attack orange and 

 coffee plantations, and have caused most serious lo.^^ses in 

 Ceylon and the Azores. In Europe, they often ruin the 

 olive crop. With a few plants to care for, the plan of 

 washing each leaf can be adopted, but the owner of an 

 estate on which thousands are grown is in a helpless con- 

 dition. These black plagues are not strictly parasites, as 

 many of their relatives are. If a slip-htly or newly-affected 

 orange-leaf, for example, is carefully washed, and then 

 examined under the microscope, its surface will be found 

 uninjured, and if the cleaning is done in time, the plant is 

 not damaged, and the leaf fulfils its functions as before. 

 If, however, the black mildew is allowed to flourish and 

 cover the whole leaf surface, as with a black felt, the leaf 

 is killed, and if a large proportion of the leaves suffer, the 

 plant may not recover. In one instance in the writer's 

 grounds, a small bush of the bay {Lauras nohilis) was 

 attacked and a great many of its leaves partially covered 

 by the fungus. Most of it was gently scraped offi and the 

 shrub seemed none the worse, but most of the branches 

 died in the ensuing cold winter, while others of the same 

 species, which were not invaded by the black enemy, did 

 not mind the frost. 



PHOTOGRAPHY FOR A3IATEURS. 



THE question of popularising photography being now 

 prominently before the public, we propose to offer a 

 few remarks bearing thereon, premising that the subject is 

 one in which many of our readers may be interested. 



Less than half a century ago the art of [ihotography was 

 regarded, by all but the very few initiated into the secret 

 of its working, as being little short of magic ; and although, 

 by the improvements it has undergone from time to 

 time it has to a certain extent become familiarised 

 with many, it nevertheless continued to be regarded as 

 an " art and mystery " by a great majority of the public 

 until within the last decade. During this period, however, 

 a change has been experienced which may be pronounced 

 as little less than a revolution, — a change which has placed 

 photography in the first rank as a study and an amuse- 

 ment. Its value as an aid to scientific research has long 

 since been conceded ; but owing to the technical difficulties 

 in working the old " wet " process, it has, till within com- 

 paratively recent times, been little used for this purpose 

 except through the professional artist. 



The change referred to consists in the substitution of 

 " dry " for wet plates in producing the negatives ; and in 

 order that those of our readers who are unacquainted with 

 the methods may understand the full significance of this 

 improvement, we will endeavour to give a rapid contrast of 

 the two processes, though considerations of space prevent 

 us from entering on a detailed description. 



By the wet process the amateur desirous of practising, 

 say, landscape photography, would have to carry about 

 with him quite a laboratoiy of chemicals, requiring very 

 delicate handling ; and if the size of the intended picture 



