174 MANUAL OF MODERN VITICULTURE. 



Summer spore. Conidia. The extremities of the fructi- 

 ferous branches swell and form the summer spores, which 

 become free at complete maturity. New spores are never- 

 born again by the same sterigmata. These conidia are 

 pear shaped, generally longer than wide, inserted at the 

 narrow extremity, constituting an agglomeration of fruit on 

 the top of the small tree formed by each filament (Fig. 

 150 e). They have a regular delicate membrane easily 

 detected and are filled with granular matter (protoplasm). 



Their excessive tenuity and lightness allow them to be 

 carried very rapidly by the wind to great distances. They 

 are from O'OIO mms. to 0*015 mms. in width and 0-015 to- 

 0*30 mms. in length. On young vines they are smaller and 

 more spherical in shape. Towards the end of the vegetative 

 season they are rather larger and filled with granular proto- 

 plasm, the membrane being less distinguishable. 



The conidia propagate the parasite during the whole 

 summer. Their vitality is not very great ; in dry climates 

 they become wrinkled and burst, completely discharging 

 the contents, as we have been able to ascertain from personal 

 experiments in the field. 



If they fall into a drop of water they germinate rapidly at 

 a temperature of 77 to 86 Fahr. The contents of the conidia 

 then become divided by dark lines into 5 to 8 fragments or 

 zoospores ; the membrane of the conidia becomes softer, 

 generally opposite its point of insertion, and, within half-an- 

 hour to an hour, gives birth to these fragments of proto- 

 plasm, deprived of membrane. 



They have an irregular shape, and are provided with two 

 cilia, inserted near a light spot which are usually detected 

 when the zoospore is about to attach itself to the cuticle of 

 a vine leaf. Helped by those two cilia they travel through 

 the liquid, whence their name of zoospore and the name of 

 zoosporangium given to the conidia or bag which contains 

 them. After they have attached themselves to the cuticle of 

 their host they become invested by a delicate, transparent 

 membrane and throw out a tube (mycelium) which per- 

 meates the intercellular spaces of the parenchyma. 



Winter spores. Ovse. (Fig. 150 d, b) : Spherical, large 

 swellings are formed on the mycelium inside the tissue of 

 the leaf, in which the protoplasm accumulates. This 

 spherical body, full of protoplasm, is the origin of the 

 female organ, and is named oogonium. The protoplasm,. 



