2Y2 



PLANT STUDIES 



fiiKilly deadened spots on the leaves, where the tissues have 

 been killed. 



From this internal mycelium numerous sporojihores 

 arise, coming to the surface of tlie host and securing the 

 scattering of their 

 spores, which fall 

 u])on other leaves 

 and germinate, the 

 new niycelia pene- 

 trating among the 

 tissues and begin- 

 ning their ravages. 

 The sporophores, af- 

 ter rising above the 

 surface of the leaf, 



branch freely ; and many of them risiiig near together, 

 they form little velvety patches on the surface, suggesting 

 the name " downy mildew." 



6 f 



Fig. 'SA'.\. a hrancti of Peronospora in contact with 

 two cells of a host ])lant, and sending into them 

 its large hanstoria.— After DeBakt. 





Y\f.i. 2iO. Pi rcncsjior'/, <"nie of the Phycoinyrcirs, showiiiL: at a an o<igoniinn io) con- 

 taining an egg, and an antluTidinni in) in eontiict; at b the andicridial tulio pene- 

 trating the oogonium and discharL^dng the cdntents (if the antheridiuni into the 

 <'gg; at r the oogonium containing tlie oospore or re.-^ting sjiore.— After DkRary. 



In cortain conditions special hranclies arise from the 

 mjcelinm, whicli organize Jintheridia and oogonia, and 

 remain within the liost (l*'i,u". "-MO). '^Flie oogonium is of 



tli(.' usiiaJ spiici'ical form, cru'a.iiizini;" a single vj^tx. The an- 



