242 PRACTICAL BOTANY 



III. Tease out a portion of the infected part, as well as of the 

 healthy part above, with needles in water, and mount so that a 

 part at least of the epidermis shall be seen in external surface 

 view ; or sections may be cut, the infected part being held 

 between pieces of pith : in such preparations observe 



1. The healthy part of the epidermis with elongated cells, and 

 occasional stomata. 



2. The branched, highly refractive, and for the most part non- 

 septate hyphse, running with an irregular, but mostly longitudinal 

 course along the outer surface. 



3. Mark especially the points of entry of the Fungus into the 

 host-plant : this may be either 



a. By perforation of the outer wall of a cell of the epidermis ; 

 and this is by far the more common : or 



b. By passage of the hypha through the pore of a stoma : this 

 is the less common mode. 



4. Trace the further course of the hypha through the trans- 

 parent tissues of the host-plant, noting the rarity, or complete 

 absence of septa. 



IV. Place an infected seedling in fresh water, in a flat watch- 

 glass, and examine it at intervals for a day or two under a low 

 power. Many of the filaments will be seen to form swellings at 

 certain points, which assume a spherical form, are filled with 

 granular protoplasm, and are divided off by a septum from the 

 parent filament, while the thin outer wall assumes a darker 

 colour : these swollen bodies are the asexual reproductive 

 organs, or resting conidia. Two types are to be dis- 

 tinguished 



1. Terminal conidia, at the ends of the filaments. 



2. Interstitial conidia, which may appear at any other point 

 on the filament. 



It is characteristic of this species that the hypha should be 

 partially or completely emptied of protoplasm for a short dis- 

 tance below the conidium. 



These conidia are capable of withstanding drought, or a 

 temperature below freezing, without losing their vitality. 



V. From a culture containing numerous conidia, separate a 

 small portion, and expose it in a watch-glass to a relatively con- 



