256 ROMANCE OF LOW LIFE AMONGST PLANTS. 



plants, and spread dismay amongst cultivators of 

 garden produce, are those which have been called 

 "rotting moulds" — such as the potato-disease, and a 

 similar disease on spinach, lettuces, and green onions. 

 All these several diseases are .eminently destructive, 

 and all are so much alike in their structure and life- 

 history that the description of one may, in all essen- 

 tial particulars, be likewise applied to the others. 

 They are included here in order to demonstrate the 

 elaborate system which is developed in plants so 

 minute, for the continuance of the species, and to 

 give some idea of the difficulties in the way of eradi- 

 cating or mitigating the disease when it has once 

 obtained a footing. The first external evidence of 

 the presence of these fungi will be found in their 

 sickly appearance, and the speedy appearance of 

 mouldy spots on the leaves and stems, frequently the 

 under surface of the former, resembling patches of 

 meal, but soon revealed to be effused clusters of delicate 

 threads of mould, crowned at their apices with myriads 

 of spores. This is the first condition which presents 

 itself to the naked eye, but before this occurs the 

 great mischief has been done, and the parasite has 

 established itself effectually throughout the tissues of 

 the host plant. 



As a starting-point we take one of the spore bodies, 

 or conidia, which are developed in such profusion on 

 every fertile thread of these tufts of mould when 

 mature. This conidium is an elliptical, or subglobose, 

 colourless minute body, having a thin smooth outer 

 coating of membrane, enclosing the fluid contents. 

 These contents, or plasma, soon become granular, 



