1895.] Development of Uncinula. 491 
of the perithecium after being ruptured. The perithecium is 
doubtless filled to the point of bursting, pressure being great- 
est just over the apices of the asci. The least disturbance at 
this stage will cause a rupture at the point above noted and 
immediately the asci begin to go in the direction of the least 
resistance. During the passage of the thickest part of the 
ascus (z. ¢. the top), it moves quite slowly, and at this time 
the ruptured edges of the perithecium are pushed a little fur- 
ther apart. As soon, however, as the tapering portion of the 
ascus is reached there is a sudden contraction of the more or 
less elastic perithecial walls and in consequence the ascus is 
ejected with considerable force. After April Ist it was diffi- 
cult to find perithecia containing spores and before the end 
of the month they had entirely disappeared. A number of at- 
tempts were made to infect grape and Ampelopsis leaves 
with ascospores, but the results of this work were in every 
Case negative. 
In conclusion I wish to express my thanks to Mr. D. G. 
Fairchild, my former assistant, who made a number of the 
sketches upon which the finished drawings accompanying this 
Paper are based, and who also aided me in other ways. 
Division of Vegetable Physiology and Pathology, 
U. S. Department of Agriculture, Washington, D. Be 
EXPLANATION OF PLATES XXXII anp XXXIII. 
T surface of haustoria.—Figs. 3 and 4. Haustoria within the epi- 
dermal cells of Ampelopsis quinquefolia.—Figs. 5 and 6. Chains of 
conidia.— Fi Isolated conidia.—Figs o. Germinat- 
ig > ; 
Spores, drawn just before the escape of the latter.—Fig. 23. Germl- 
