408 



BOTANY OF THE LIVING PLANT 



to the parasitic life. It is thus impossible to lay down any general 

 rule of priority for parasitism or saprophytism : and it is only in 

 certain cases that the one habit or the other can be assigned to any 

 definite systematic group. 



The life of Fungi is very varied. No organisms show greater resource 

 in the acquisition of food. But their propagative methods are no 

 less effective. Originally sprung from aquatic organisms, some 

 show this clearly in their reproductive organs, which often involve 

 motility in external water, as in many Phycomycetes. But the more 

 advanced types are commonly propagated by means which are clearly 



FIG. 343. 



Portion of the root of a Crucifer malformed owing to the presence of Plasmodiophora. 

 (After Woronin ; from Marshall Ward.) 



related to life in the air. In most Eumycetes minute bodies called 

 conidia are borne in prodigious numbers, and they are small enough 

 to be carried as dry dusty bodies through the air. The conidia of 

 common Moulds are present everywhere about the dwellings of man : 

 so that any suitable medium is apt to be invaded by them, provided 

 the conditions of temperature and moisture are favourable. This 

 explains the apparently spontaneous appearance of moulds on bread, 

 leather, jam, etc., when kept in a confined space. The spread of 

 fungal diseases is usually by similar means. One of the most surprising 

 facts in this relation is the very constant recurrence of certain Fungi 

 on isolated and restricted media. The horns of sheep cast away 

 on a Scottish hill-side are commonly invaded by a horn-destroying 

 Fungus, Onygena. But any one such horn may be isolated far from 

 any visible source of infection. This shows tke ubiquity of fungal 



