204 Commercial Gardening 



According to their mode of attack the parasitic fungi are divided into 

 two groups: (1) the epiphytic and (2) the endophytic. The latter penetrate 

 the tissues of the plant and there develop their mycelium; the former 

 vegetate on the surface and spread their mycelium over it. 



The mycelium constitutes the typical vegetative structure of a fungus, 

 and is of a thread-like and much -branched character. The threads of 

 which the mycelium consists are called "hyphae". In some forms of 

 fungi, however, there are no threads, but separate cells, as in the Yeast 

 Plant. The mycelium (or its hyphse) may be one-celled, or it may be 

 divided transversly into separate compartments, each of which may con- 

 tain several nuclei from which in due course spores may develop. When 

 the hyphse of some fungi branch between the cells of plants, they often 

 develop. Generally speaking the visible part of a fungus is the " fruiting" 

 part, from which fresh spores are distributed when ripe, and are carried 

 from one place to another by the wind and water. In such fungi as the 

 Common Mushroom, the so-called Toadstools, the Beef-steak Fungus, and 

 many other conspicuous plants, the spores may be readily collected if the 

 "caps" of the fungi are placed on sheets of paper in a warm room, and 

 may be easily seen with the naked eye. In the case of the fungi that 

 attack our plants, however, the spores and even the entire fungus pro 

 ducing them are very minute, and require powerful microscopes to distin- 

 guish some of their special feeding or absorbing organs, called "haustoria", 

 which penetrate the cell walls and absorb the nourishment from the cells. 



It is thought that fungi originally came from the Algse, and have 

 undergone various changes in the process of evolution. A fungus begins 

 life from some kind of a spore of a very simple character, quite distinct 

 in character and structure from the seed of a flowering plant. When the 

 spore of a fungus germinates on a suitable plant tissue it swells up by 

 absorbing moisture and sends out a germ tube, which penetrates the host 

 plant and as it lengthens and branches becomes the mycelium or spawn. 

 After a time the mycelium begins to give off fresh spores, varying in form, 

 development, numbers, &c., according to the different kinds, and known 

 by specialists under different names. The various spores of fungi may 

 arise from the sexual union of two distinct cells, or they may originate 

 asexually by means of "swarm" spores. Under certain unfavourable 

 conditions the spores of fungi may remain dormant for a considerable 

 time, but possess the power of germinating afterwards under favourable 

 conditions. It is the resting power of the spores of many fungi that con- 

 stitutes the chief danger to the cultivator, as he never knows how many 

 thousands of them may be sleeping in his soil. For certain pot plants, 

 like Ferns, it is possible to sterilize small quantities of soil by pouring 

 boiling water over it, or by roasting it in a furnace; but such operations 

 are quite beyond the range of practicability with large quantities of soil. 

 The nearest approach to sterilizing the soil in the open air, and preventing 

 the spread of fungoid diseases (as well as insect pests), is to cultivate 

 frequently and strew powdered sulphur over any areas known to be badly 



