OOPHTTA. 



141 



oogones) tecome greatly tHckened and finally assume a 

 globular shape (Fig. 69, o); the other branches (the young 

 antherids) become elongated and club-shaped (Fig. 69, w). 



^nru 



Fio. 68.— Giermination of the conidia of Potato-mildew, a, 6, c, formation of 

 zoSspores; d, growth of zoospores; sp, a zoSspore growing into the cells of the 

 plant, e, i. Magnified about 400 times. 



The antherids bend and come in contact with the oogones, 

 and soon each thrusts out a small tube which penetrates 

 the oogone, reaching the germ-cell. The protoplasm of the 



Fie. 69.— Sexual organs of a Mildew, », oSgones; n, antherids. .^.youngest 

 stage; B and C, older stages. Magnified 350 tunes. 



antherid is thus transferred directly to the germ-cell (Fig. 

 69, A, B, C). After fertilization the germ-cell secretes a 

 thick double wall, and so becomes a resting spore. 



294. The resting spores remain in the tissues of the host 

 until the latter decay, which is generally in the spring. 



