August, 1910.] 



125 



Plant Sanitation. 



The fungi form a subdivision of the 

 plant kingdom. The group consists of 

 several thousand species of plants, which 

 differ enormously in size, structure and 

 complexity. They are grouped together 

 for several reasons, as for example, the 

 similarity of their vegetative parts, the 

 fact that they are all reproduced by 

 means of spores, and that all of them, 

 without exception, have entirely lost 

 the power of forming chlorophyll— the 

 green colouring matter which occurs in 

 all other plants, with but few exceptions 

 and without which the plant is unable 

 to elaborate its own food-supply from 

 the carbon dioxide and oxygen contained 

 in the air. For this reason, the fungi 

 may be looked upon as a degenerate 

 group of plants, that is, when regarded 

 from the standpoint of the main path of 

 evolution ; in their own line, however, 

 they have attained very considerable 

 complexity in their reproductive arrange- 

 ments, and also show many and varied 

 forms of adaptation to the manner 

 of life which they have been driven 

 by different circumstances to adopt. 

 Members of this large assemblage of 

 plants may be found living under the 

 most various circumstances of temper- 

 ature and moisture, and with widely 

 different sources of food-supply. 



It will now be apparent that a term 

 which is applicable to so many and so 

 various forms of plant life can hardly be 

 expected to possess in reality the narrow 

 significance indicated in the opening 

 paragraph, 



The subject may be further considered 

 at somewhat greater length from a 

 different point of view. Since the fungi 

 are unable to obtain their own food 

 supply from the air, it follows that they 

 must obtain it already manufactured 

 from one or more sources. The only 

 organism that can manufacture its own 

 food supply from the air is the green 

 plant, so that, clearly, one possible 

 source of food to the fungi is the bodies 

 of such plants, either alive or dead ; 

 moreover, since animals may be regarded 

 as fundamentally dependent on green 

 plants for their food supply, their dead 

 or living bodies also offer a possible 

 source of food to the fungi. These are 

 the only available food supplies for these 

 plants. 



As would be naturally expected, all 

 four sources of food, namely, living and 

 dead plants and living and dead animals, 

 are utilised by different species of fungi. 

 Those fungi which live on dead plants 

 or animals, or on the products of the de- 

 cay of such, are known as saprophytes ; 

 while those that obtain their food from 

 living sources are known as parasites. 



There is an intermediate class, the facul- 

 tative parasites, which can attack some 

 living plants, or can, if necessary, live on 

 dead vegetable matter. 



Although these are the more technical 

 divisions of the fungi they may be con- 

 sidered differently in their relation to 

 agriculture. In this connection, there 

 are three points of importance. Firstly, 

 there is the damage that they cause ; 

 secondly, the advantages that some of 

 them confer ; and lastly, the develop- 

 ment of which these advantages are 

 capable. 



Some of the forms that grow on animal 

 vegetable products — saprophytes— are a 

 source of annoyance and loss to mau, 

 as for example the moulds that grow on 

 grain, bread, cheese, and other eatables, 

 or even on cloth and leather. These 

 may, however, be kept in check with- 

 out much difficulty. Among the facul- 

 tative parasites, many species can 

 attack the roots of various economic 

 plants, and even if they do uot 

 actually bring about the death of their 

 hosts, they weaken them to such an 

 extent that the value of the crop 

 produced is greatly diminished ; more- 

 over, their power of living on decaying 

 remains of these hosts, or even on those 

 of other plants, renders them extremely 

 difficult to eradicate, once they have 

 obtained a hold. Among the class 

 known as parasites are included all those 

 forms understood by the term Fungus 

 in its more narrow application. They 

 are undoubtedly a source of great loss to 

 all those interested in agriculture, and 

 even when the greater part of the loss 

 can be obviated by the employment of 

 sound preventive measures, the carr ying 

 out of such measures involves the expen- 

 diture of considerable sums of money. 



On the other hand, many species are of 

 considerable service to man, for several 

 of them help to destroy old plant and 

 animal remains, and in this way act as 

 scavengers. They may, for example, 

 live on heaps of dead leaves, old tree 

 stumps, decaying branches, or any 

 other accumulations of rubbish. They 

 often possess the power of secreting 

 enzymes, which can dissolve various 

 forms of organic matter not otherwise 

 easily destructible. The products of 

 their action go to increase the humus 

 content of the soil, often in forms in 

 which they are available to higher 

 plants as a source of food. Such fungi 

 must be regarded as useful, both in 

 their capacity of scavengers, and in 

 their function of suppliers of humus 

 products to various crops. Other species 

 can live on harmful fungi, and are useful 

 in this way, while still others are para- 



