392 DIVISION III. — MODE OF LIFE OF THE FUNGI. 



of a foliage-leaf which stands underneath an inflorescence, generally the next but one 

 or two beneath it ; the leaf or leaves above it and the inflorescence itself wither away in 

 consequence. 



In this and in almost all the cases of the Peronosporeae and Ustilagineae 

 wliii li have been mentioned the mycelium spreads through the entire stem 

 of the plant but cannot be seen in it, and causes no change in it which is visible 

 from without. A superficial examination only would lead us to suppose that only 

 the parts chosen for the formation of spores are occupied by the Fungus, and that 

 the rest of the plant which looks quite healthy is free from it. But in most cases of 

 the kind all or nearly all the similar parts of a plant where spores are formed by 

 preference are seen even in their young state to be uniformly occupied by the spore- 

 forming organs of the Fungus. This enables us to conclude in doubtful cases that 

 the Fungus is one which is widely spread and not confined to a limited spot, because 

 in the latter case it scarcely ever happens, for obvious reasons, that all similar young 

 parts are attacked in this uniform manner. 



Section CXII. Independently of these coarser phenomena of localisation 

 the histological distribution, as we may briefly term the behaviour of the Fungus 

 to the cells and tissues of the host, is also liable to variations in endophytic 

 parasites on plants and in the endophytic haustoria of parasites which are otherwise 

 epiphytic. In considering these variations we must of course also keep in view the 

 reactive influence of the host, which is necessarily connected with them. 



In the higher plants with their various kinds of tissue the wood-destroying 

 Fungi described at page 383 spread in the tracheal and sclerenchymatous tissues and 

 destroy them. But most parasites exclusively or almost exclusively attack living cells 

 containing protoplasm, the parenchyma therefore, soft bast and epidermis, where the 

 tissues are differentiated, and even the wood-destroying Fungi just named do the 

 same. Accordingly a number of histological localisations result from conditions such 

 as have been already described, and further details must be sought in special treatises 

 on the subject. But as a topic of general interest we must briefly notice the 

 differences in the behaviour of endophytic parasites to the living cell. 



In unicellular hosts an endophyte is necessarily intracellular, that is, vegetates 

 inside the cell. It may also be intracellular in pericellular tissues, but it may also 

 spread in the intercellular spaces, or it may exhibit both modes of distribution. When 

 its growth is intercellular, it stands of course in the relation of an epiphyte to the 

 individual cell, and of that we need say no more here. The entry of the parasite 

 into the cell of the plant or into parts of it takes place in very dissimilar forms and 

 with very dissimilar consequences. 



To begin with the extreme which lies nearest to the superficial view of the 

 subject, there are many parasites whose hyphae penetrate through the membrane 

 and into the protoplasmic body of the cell, and kill and destroy the latter at once; 

 examples of such Fungi are seen in all the facultative parasites described above, 

 Sclerotinia and Pythium and their near allies the Phytophthoreae and others ; 

 Ancylistes is an instance of this in unicellular plants (page 139). 



Other parasites also penetrate the membrane of the cells and pass through 

 them and through the protoplasmic body. But the latter docs not at first succumb to 

 the assault of the parasite, but retains the qualities which it has in the living cell, and is 



