294 



The Plant World. 



water, the swelling of cell membranes and of certain cell contents, 

 as a result of which a highly efficient stimulus is brought to bear. 

 The exact processes involved in the action of this stimulus arc 

 not yet investigated. 



Nadson, in the Jahrb. f. Pflanzenkrankheiten, records the 

 wholesale destruction of oak seedlings in one of the districts of 

 Russia, which is attributed to disturbed symbiosis, the mycor- 

 rhiza growing on the roots of the seedlings having become para- 

 sitic through the influence of unfavorable conditions. A similar 

 condition of affairs has been observed in the chestnut. In gen- 

 eral it appears, according to the author, that a mycorrhiza fun- 

 gus is in its essential nature a parasite, but that its parasitism 

 is commonly restricted to the outer cell layers of the root, and that 

 it brings some advantages to its host by supplying water and 

 food substances; there are cases, however, such as those cited, 

 in which it becomes an aggressive parasite and is highly de- 

 structive. 



In Science for Nov., 1909, Professor George J. Peirce writes 

 of the possible effect of cement dust on plants and records his 

 observations in the vicinity of Concord, Cal., where a manu- 

 factory of Portland cement is operated. It appears probable that 

 the injury to vegetation is much greater where, as in southern 

 California, there is no rain for the entire summer, after the leaves 

 of deciduous plants have developed, than it would be in regions 

 of abundant rainfall through the growing season. 



In the same number of Science, H. A. Anderson gives an ac- 

 count of investigations of algae of the Upper Cayuga Lake 

 Basin and offers some interesting suggestions regarding the pos- 

 sibility of the cultivation of Spirogyra, Chaetophora, and some 

 other green algae on a sufficiently extensive scale to provide 

 food for certain aquatic animals that, in their turn, serve as food 

 for fishes. 



In Muhlenbergia for September, 1909, S. B. Parish con- 

 tributes notes on some introduced plants of southern California. 

 These notes have the value of personal observations carried on 



