202 The Plant World. 



1. The greater number of forms which are present in 

 orchards during the autumn, winter, and spring are saprophytic, 

 the most common being Alternaria sp., Cladosporium sp., and 

 Penicillium expansum. 



2. Phyllosticia limiiata, a parasite, and a very common 

 cause of leaf-spot of apples, is present in abundance during the 

 entire winter period, regardless of temperature. 



3. Nummularia discreia, although the fruits are mature, 

 does not disseminate its spores until May. 



4. At no time during the period in which exposures were 

 made (September to May, inclusive) were viable spores of 

 Sphaeropsis malorum present in the atmosphere of the orchard. 



5. The total number of spores in the air of orchards is 

 influenced by the ground cover, being less in well kept, and 

 more in neglected orchards. 



BOOKS AND CURRENT LITERATURE. 



Marloth has recently published in the South African Journal 

 of Science a study of "The Vegetation of the Southern Namib" 

 which deals with an area approximately 50 miles wide, lying 

 about 100 miles north of the Orange river, characterized as a 

 "waterless desert" and presenting certain striking features of 

 vegetation which can be definitely correlated with environmental 

 factors. Among the most interesting cases may be mentioned 

 the trimming eflFect of the wind. On the rocky hills small shrubs 

 of Pteronia or Salsola are trained into a narrow, sharp-edged 

 wedge, ten times as long as broad and closely pressed to the 

 ground, the main stem being bent over at a right angle immed- 

 iately above the projecting stone or pebble, behind which the 

 plant had started its growth. This and additional vivid descrip- 

 tion given by the author call to mind the precisely similar phe- 

 nomena which travelers by the Southern Pacific may observe 

 in the northern part of the Colorado desert. 



Hryniewiecki reports in a natural history publication of the 

 University of Dorpat the results of his investigations of rheo- 

 tropism of roots conducted in the botanical laboratory of Leipzig. 

 It appears that rheotropism is most pronounced in all cases 



