Vol. VIII. No. 190. 



THE AGRICULTURAL NEWS. 



251 



FUNGUS NOTES. 



In continuation of the infonnation contained in an 

 article in Vol. II, No. 22, pages 61-2 of the Acjriculta- 

 ral N'eiV'i, it is intended to publish, in this and the next 

 two numbers, a short article giving an account of the 

 principal points of interest in the life-history of the 

 luncri, and to indicate their connexion with practical 

 agriculture. The present number contains the nrst oi 

 these. 



PART I. 

 SroRES. Their Foematicn and Purpose. 



All publications on the suViject of plant diseases caused 

 by fungi include .some reference to the spores produced by 

 the parasites, and indicate that it is by means of these spores 

 that a fungus is able to spread. Consequently, the prevalent 

 idea is that the .spore is a form of seed, though very small. 

 This idea is to a certain extent correct, but in one or two points 

 there is a fundamental difference between the two, as will 

 appear later. 



The simplest type of spure formation is as follows. 

 A single thread, or hyplui, as it is called, of the fun- 

 gus swells slightly at the end and becomes very full 

 of protoplasm ; it then becomes constricted just below the 

 tip, and this constriction proceeds until the tip is completely 

 cut off in the form of a round or o\'al spore (see Fig. 1). The 

 .s[>ore contains a nucleus and dense protoplasm, and is usually 



Fio. 1. 

 surrounded by a firm, smooth wall or coat. Such a spore is 

 nothing more or less than a small portion of the original 

 fungus plant, and is really more properly compared to the 

 bud of a plant than to a seed. 



It is true that the seed and the spore have certain 

 points in common. Both serve the purpose of reproducing 

 their kind and, also, both are adapted for dispersal, so as 

 to prevent competition with the parent. Again some 

 forms of spores, and most seeds, are capable of existing 

 under very adverse circumstances such as extreme drought, 

 or excessive cold, which will kill the parent plant, and the 

 continuation of the species is by this means made certain ; 

 for this purpose they both contain supplies of reserve food- 

 material. Here the similarity ceases. The fundamental 

 difference is that the seed of a flowering plant always 

 contains a small complete plant, or embryo, while a spore 

 never does, but usually consists of one cell which can produce 

 a new plant. Besides this, owing to cross-fertilization, it is by 

 no means necessary that the young endiryo in the seed will, 

 when full-grown, exhibit the same characters as the mother 

 plant on which it was borne, while the spore, being usually 

 merely a piece of the original individual, is bound to be 

 exactly like that individual. Even when spores are produced 

 sexually as is sometimes the case, the sexual processes are 



between two parts, often closely related parts, of the same 

 individual ; this might be compared broadly to self-fertiliza- 

 tion in flowering plants, and consequently, the resulting 

 plants are very like the parent. 



Thus there are usually two forms of spore produced liy 

 a fungus. The method ot^ production of the first has already 

 been described for the simplest ca.se. These spores are 

 carried by the wind or insects to a suitable place, as for 

 example, some definite host plant, where they germinate at 

 once, thus ensuring the increase in numbers of that species 

 of fungus. But as circumstances often become unfavourable, 

 owing, usually, to the exhaustion of the food supply on 

 which the fungus is growing, or to adverse conditions of 

 weather, another form of spore may be produced. The forma- 

 tion of these spores often entails a very simple form of sexual 

 union. To illustrate what is meant, the process exemplified 

 by the Mucors, or mould fungi, may be described. Two 

 hyphac from the same plant, lying near one another, become 

 swollen at the ends. These ends grow towards one another, 

 touch and finally fuse together, the wall between them 

 being absorbed. The nuclei then unite and the fused tips 

 are cut off by cro.ss walls in the hyphae. Xext, the outside 

 of the spore thus formed becomes hard and warty and, in 

 thi.-i way, a spore is produced with dense contents, some 

 reserve food, and a thick coat, which is capable of existing 

 under adverse circumstances, and which \\\\\ not begin to 

 grow again till several weeks or months have elapsed, and 

 circumstances are again favourable. Such resting-siiores are 

 often coloured owing to the piresence of coloured oils, or to 

 the colour of the thick coat. 



Fni. 2. 



Other methods by which such spores are produced are 

 mainly modifications of th.ot by which the quick-growing form 

 arises, only that for resting-spores the contents are denser, and 

 the coat is always hard, and often ridged or warty on the out- 

 side, as has been stated. A similar kind of spore is that pro- 

 duced by the fungus causing rind disease of the sugar-cane, 

 CoUetotricliuiit. falcatiiin. T'nder adverse circumstances, the 

 walls of any cells of a hypha of this fungus, inside the host 

 plant, can become covereil with a hard coat, and .so form 

 resting-spores. An example of this is shown in Fig. 2. The 

 cells shown with thick walls are resting-spores, which have 

 germinated to form the kind of spores first described. 



It is clear, then, that the first or quick-growing kind of 

 spore is directly responsible for all epidemics, and is hard to 

 deal with, once it has gained a hold, owing to the immense 

 numbers in which it is produced. But the second form, 

 which is often much less numerous, is really more important, 

 as it is responsible for the contiimation of tlie fungus from 

 year to year, and it is the presence of this form of spore in 

 particular which makes the destruction of all diseased 

 material, especially at the end of a crop, a matter of such 

 vital importance to the planter. 



