THE HAMILTON ASSOCIATION. 



87 



fXy 



tissue except that it 

 sends down among 

 the cells occasional 

 suckers (see fig. 12, 

 b. b.), by which it 

 draws nourishment. 

 That the threads of 

 the mycelium are not 

 easily distinguished is 

 evident when we note 

 Prof. Scribner s state- 

 ment that they are 

 each only one six- 

 thousandth part of 

 an inch in diameter. In June or July short upright branches ap- 

 pear, which are jointed, as shown in Fig. 12. One by one these 

 terminal cells drop off. They are really summer spores for the pro- 

 pagation of the mildew, and are known as conidia. Two of these 

 are shown in fig. 12, a. a., which, according to Prof. Scribner, are 

 only one-thousanth part of an inch in length at their largest diamt" 

 ter. These float about in the air, and alighting on a proper host 

 soon germinate under the favoring conditions of summer heat and 

 moisture. 



CL^ 



Fig. 12.— Mycelium of Uncinula Spiralis, from a 

 grape leaf. 



Tig. 13. 



Fig. 13 shows a very small portion of epidermis of a grape 

 berry, upon which the mycehum of Uncinula has grown, highly 

 magnified. 



Later on in the season, during the months of September and 

 October, spores quite different in character are formed. The case 

 in which they grow is apparent to the naked eye, and is known as 

 the perithecium, or " fruit " of the mildew. Each of these is full of 

 asci, three of which are shown emerging from the perithecium in 

 fig. 14. Inside these, in turn, are the ascospores, or winter spores. 



