208 



The Botanical Gazette 



[J«iy. 



BRIEFER ARTICLES. 



Penetration of the host by Peronospora g-angrlitbrmis.— While 



studying the lettuce mould in the fall and winter of 1890, some obser- 

 vations were made by the writer on the penetration of its germ-tubes 

 that differ from those heretofore recorded. 



Spores of the fungus were sown in a drop of water upon the under 

 surface of leaves of lettuce {Lactuca saliva). The leaves were kept in 

 a moist atmosphere under a bell-glass in the laboratory. After twenty- 

 four hours pieces of the epidermis were stripped off from the infected 

 spots and examined under the microscope. The spores had germin- 

 ated abundantly, pushing out a strong germ-tube into which the pro- 

 toplasm of the spore haa passed, leaving the empty, and often 

 shriveled-up spore membrane attached to the germ-tube. 



Several cases of penetration were seen, the germ-tubes pushing their 

 way between the guard-cells of the stomata (figs, i, a and 3). In other 

 instances the germ-tubes had approached quite up to a stoma, but had 

 not yet penetrated (fig. 2 ). Very many of the germ-tubes had grown 

 straight forward for a time, and had then made a rather sudden turn, 



directing the terminal portion toward a stoma in the vicinity (figs- * 

 and 4). 



