DISPERSAL BY WIND. 



823 



where they touch the ground, and at the same time send up new lateral branches 

 from the opposite side, as shown in fig. 455. It should be mentioned that in K. 

 articulata the roots often begin to develop before the branches have broken and 

 fallen off, always appearing on the side of the shoot which is turned towards the 

 soil. This also is shown in the figure. 



Fig. 455. — The formation of oifsiioots iu Eleinia artuvlata. 



In all these instances the offshoots are detached by the force of the wind. 

 Another method by means of which the same end is attained depends on the 

 hygroscopic properties of the tissues concerned, and on the alternate swelling and 

 contraction from this cause. Several Fungi of the group Peronosporeee, among others 

 the unwelcome Potato-disease Fungus, Pliytophthora infestans, multiply by spores 

 formed on delicate hyphal threads, which are protruded from the stomata of the 



