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INTRODUCTION TO THE STUDY OF FUNGI 



complex fructification. The disease which has for some years 

 attacked the potato, and at one time was called the " potato 

 murrain," is of this character. This disease is unfortunately 

 present, and deeply hidden in the tissues of the plant, before 

 any external evidence is manifest. When the fructification 

 appears, usually on the under surface of the leaves, it occurs 

 on vaguely circumscribed patches, which become discoloured 

 and soon rot away. The mycelium pervades the entire plant 

 more or less, but especially at the point of issue. The erect 

 conidia-bearing threads issue singly or in bundles through the 



Fig. 44. — Stages of germination of a conidium or sporangium of Phytoph- 

 thora. a, rii^e condition ; h, contents breaking up into blocks ; which 

 escape, c, d ; zs zoospores, e ; with two cilia, /, g ; zoospores at rest, 

 g, h ; and germinating, i, j, k. After Marshall Ward. 



stomata, soon becoming branched towards the apex once, twice, 

 or several times in a furcate manner, the tip of each ultimate 

 branch bearing a single oval or elliptical hyaline conidium, or, in 

 the present case, a sporangium (Fig. 44). When mature these 

 sporangia, for the most part, become granular within, and at 

 length the granules accumulate in definite spots, and finally 

 become invested with a delicate membrane ; so that when the 

 parent membrane ruptures and the contents escape, they do so in 

 the form of an uncertain number, it may be four or six minute 

 rounded bodies, each furnished at one end with a pair of 

 delicate movable hairs. As soon as these are liberated and 

 they encounter a thin film of moisture, they float away, being 



