24 SEXUAL REPRODUCTION IN CERTAIN MILDEWS. 



is covered by a layer of these oval vesicles. It is possible that the vesicles 

 burst and exude a slime more liquid than that of the deliquescent walls 

 at the time when the perithecium is overturned, and thus aid in making 

 more certain that it shall stick fast to any object which touches it. In 

 this gelatinous cap, when the perithecia are ripe, the hyphse of molds 

 may frequently be found growing. The functions and adaptations of 

 this slime-cap have been fully discussed by Neger (68), and I need 

 not go into the matter further here. 



The appendages arise in a zone about the equatorial region of the 

 perithecium as swollen cells of the peripheral layer. As has been many 

 times described, in their mature condition they consist of a slender, 

 straight spine with a very much enlarged bulbous base. They grow 

 horizontally outward in a bristling phalanx about the middle of the 

 fruit body. As it ripens they bend downward and, pressing on the leaf 

 surface, lift the fruit up, tearing it loose from its stalk and the second- 

 ary mycelial filaments described above. It is thus set free to fall or be 

 blown by the wind until it strikes and adheres to some object by the 

 mucilaginous cap described above. As a matter of fact, what seems 

 frequently to happen is that the perithecium simply rolls over and 

 remains sticking wrong side up on the same leaf on which it grew. 



The walls of the appendages very early become hardened and 

 brittle, so that they break up in cutting, and it is not common to find 

 good entire longitudinal sections of them in microtome preparations. 

 Still, their structure is very clearly shown. They contain an apparently 

 living protoplast until late in the ripening of the perithecium. As a 

 rule they have only one or two nuclei. It is quite common to find the 

 single nucleus lying, not in the bulbous base, but somewhere in the basal 

 region of the spine. The cytoplasm consists of a thin lining layer just 

 inside the wall and large vacuolar cavities filling the greater part of the 

 bulb and extending into the spine. The thickening of the wall is char- 

 acteristic and especially adapted for producing the motions of the 

 appendage, as noted above. The spine is thick-walled throughout, its 

 apex being without a lumen for some little distance. The bulb is thick- 

 walled over its upper surface, but on the under side there is an oval 

 region whose wall has remained thin. This thin area extends up on 

 the sides of the bulb also. The functioning of the structure so formed 

 is very simple. As the perithecium loses water dries out in beginning 

 to ripen the appendage loses water also by evaporation. This results 

 in a pushing in by atmospheric pressure of the thin area on the bottom 

 of the bulb and a consequent pulling down of the end of the spine as 

 a result of the shortening of the under surface of the bulb. If the 



