Vol. VIII. No. 192. 



THE AGllICULTUllAL NEWS. 



283 



FUNGUS NOTES. 



The following article is the last of a short series 

 giving an account of the principal ])oints of interest in 

 the life-history ot the fungi, and indicating their con- 

 ne.xion with practical agriculture. The first two of 

 these appeared in the two most recent numbers of the 

 Agricultural Neius, p. 251 and p. 267. 



PART III. 



The Feu it Konv? 



The simple.st form of asexual fructification in the fungi 

 is the conidii'in, or simple spore cut oti' from the tip of 

 a h3pha, as <lescribed in the first article of this series. In 

 the mould fungi the spores are borne in a receptacle, called 

 a sporangium, which forms a swollen knob at the end of an 

 erect hypha ; some of these have a mechanism Ijy means of 

 vdiich the sporangia can be driven to a considerable distance 

 from the plant which forms them. The sporangial wall is 

 sticky, and consequently adheres to any substance it may 

 hit : the gummy substance on the outside then hardens, and 

 keeps it firmly attached to whatever it comes in contact 

 •with. 



In the next higher group of fungi the spores are borne 

 in an elongated sackdike sporangium known as an asc/is. 

 Each ascus contains a definite nundser of spores, usually 

 eight. The asci themselves may be borne in a closed bo.x 

 built up of closely-woven hyphae, or on the upper surface 

 of a more or less fiat structure formed, like the box, of closely- 

 woven hyphae. The asci are always borne closely packed 

 together, and frequently large swollen hyphal hairs occur 

 between them. 



In the forms with a flat, platedike fruit-body, the asci 

 open at the top by means of a pore, or a cap-like portion is 

 removed, and the spores are forcibly ejected to .some distance, 

 owing to the mutual pressure of the asci on one another. In 

 those forms in which the asci are enclosed, a small opening 

 is formed in the top of the box, and as its contents swell up 

 ■when the spores are ripe, the latter are extruded through the 

 hole. In some cases the fruit-body remains closed, and the 

 .spores are only liberated when it decays. These boxes may 

 occur separately on the surface of the 'food substance, in 

 ■which case they are often very minute ; or many of them may 

 be borne sunk in a firm, hard tissue built up by the hyphae 

 of the fungus, and known as a stroma. This stroma often 

 forms first a simple kind of free abstricted spore from surface 

 hyphae, and then from more internal tissue produces the 

 more elaborate boxes containing the asci. 



All these forms of fruit bo'ly ma-y be coloured ; red, 

 yellow, white or black are the most usual colours. Hard 

 black patches are often found growing on trees ; these are 

 the stromata of a fungus. The fungus causing canker of 

 cacao forms red fruiting bodies, and one of the forms 

 pai'asitic on scale insects is greyish white and built up of 

 a number of nearly spherical himps, or boxes. The rind 

 disease of the sugar-cane usually appears as a number of 

 small black dots, often extruding a Idack ribbon con.sisting 

 of millions of spores held together by mucilage. 



The group of fungi mentioned abnve are known as the 

 Ascomycetes on account of the presence of the usually eight- 

 spored ascus. 



Another group of fungi known as the Rusts or Uredineae 

 form four kinds of spores. Two of these are produced in 

 pustules or sori. The pustules originate under the skni of 

 the leaves and the stems of the host jilant, for all these fungi 

 Are parasites, and eventually break through, forming short 



rusty or blackish streaks on the leaves. Another form of 

 spore is borne in small round cups often surrounded by the 

 torn skin of the host jilant, fur like the other spore-forms the 

 cups originate under the .skin. 



The fructifications of the next group of fungi are almost 

 too well known to need much description ; these are the toad- 

 stools, puff balls and bracket fungi, all of which are included 

 in the group known as the Basidiomycetes. Hei'e there are 

 usually four, sometimes two, spores borne at the end of small 

 knobs which project from a swollen cell known as the 

 hasidiuin. In the toadstool these swollen cells are arranged 

 in a row along the sharp edge of the gills, and the spores 

 hang downwards. In the pufl'-balls all the internal structure 

 breaks down as the fructification ripens, and finally there is 

 only a case left filled with a fine powder of ripe spores. 



There is also a very large number of fungi in which only 

 one stage in the life-history is known. These are grouped 

 together as imperfect forms, and include : the cotton anthrac- 

 nose, the brown rot fungus of cacao pods, the Laxtodijihidia 

 disease of cacao, and many other forms. In some of these 

 fungi, the spores are borne, as in the Ascomycetes, in 

 a closed box, often black, sometimes red or yellow, and it 

 is believed that they are usually stages in the life-history of 

 an Ascomycete. In other forms, the .spores are cut off from 

 hyphae which are massed together into a pustule, often 

 slightly coloured. Such pustules occur in the shrunken and 

 discoloured patches on cotton bolls attacked by Anthracnose. 

 Some forms cause leaf spots ; and some are only known as 

 a loose, white mould on leaves, fruit, or decaying matter. 



Besides their characteristic fruiting bodies, the parasitic 

 fungi often produce some typical appearance in the host 

 plant, by which their presence may be recognized. Root 

 diseases always cause yellowing and drooping of the leaves 

 of the host — symptoms siuular to those shown when the host 

 is sufl:ering from drought and due to the same cause, namely 

 want of water. On stems and branches, canker areas are often 

 jjroduced, as for example, the canker of cacao ; other fungi 

 cause S'wellings or the appearance known as 'Witches' Brooms', 

 that is an excessive number of small twigs borne from about 

 the same point on a branch. In some cases, '\vhen a diseased 

 stem is cut down, the wood is discoloured, looking grey- 

 ish or brown, or it may appear soft and rotten. Green 

 stems show discoloured and, frequently, sunken and hardened 

 patches which often spread in all directions round the stem, 

 and eventually the host plant is killed. Fruits show similar 

 symptoms, or they may become soft and rotten instead of 

 hard ; usually the fructifications of the fungus do not appear 

 until the fruit is nearly killed, and the same is true of other 

 parts of the host plant. A tew fungi are known which never 

 produce anything but mycelium. 



Leaves, when attacked by a parasite, usually become 

 discoloured in spots which vary in shape but are often 

 characteristic of the dfsease ; a good example is the angular 

 leaf spot of cotton caused by a bacterium. Sometimes holes 

 are formed in the leaf, or the leaf is rusted, or covered with 

 a white mould. In short, the manifestations of disease in all 

 parts of the host are varied and numerous, but frequently 

 characteristic. 



It is hoped that what has been said in these 

 articles will prove useful to any one on the lookout 

 for disease in his crops, and will enable him, with the 

 assistance of the information given in the various 

 publications of the Department, to form some idea of 

 the method of treatment likely to be successful in any 

 given case, and of the reasons for that treatment. 



