496 PRACTICAL BOTANY . 



2. The colourless non-septate hyphal filaments, which traverse 

 the intercellular spaces, not only of the cortical parenchyma, but 

 also of the pith : note carefully the button-like haustoria, which 

 the Fungus puts out through the cell- walls into the cavities of the 

 cells of the host. 



3. Where the section has traversed the white blotch, the epi- 

 dermis is separated from the subjacent tissue by a mass of hyphal 

 filaments, each of which terminates in a chain of conidia formed 

 successively by abstriction. 



4. Frequently, and especially in material taken in autumn, the 

 sexual organs of the Fungus are to be seen borne on hyphal 

 filaments within the tissue of the host. The main characters of 

 the antheridium and oogonmm correspond to those of Pythium : 

 when ripe the ovum is covered by a dark-coloured and rugose 

 exospore, as well as by the colourless inner layers (epispore and 

 endosporc). 



Attempts should be made, by placing fresh conidia in a drop of 

 water on a slide, to observe their germination : the contents 

 divide into a number of parts, which escape as motile zoo- 

 spores. Further, the behaviour of these during germination on 

 a fresh leaf of Capsella, and the entry of the germinal tubes 

 through the pores of the stomata are to be observed. 



Oospores are also to be dissected out from the tissues of the 

 host plant in spring (i.e. after the period of rest), and to be 

 cultivated in fresh water : their germination is to be observed, 

 the protoplasm dividing into a large number of swarm-spores, 

 which escape and develop further in the same way as the 

 zooronidia. 



Observations may also be made on the Potato Fungus (Phyto- 

 phthora infestans) the mycelium of which permeates the tissues 

 of the Potato plant, while its branched conidiophores project 

 through the stomata. 



