Botany and Zoology. 255 



(Sanio'sche Balken). The structures in question, which are, of 

 course, not to be confused with the trabecule or wall-thicken- 

 ings in scalariform ducts, extend radially through the elements 

 in which they occur, and, although occasionally single, often 

 recur in a great number of successive elements in the same 

 radial row. Wherever such a series of beams occurs in the 

 xylem, a corresponding one is to be found in the phloem, the 

 two being either continuous through the cambial layer or separate, 

 both ceasing at equal distances from the cambium. After describ- 

 ing the occurrence and character of these beams Mtiller proceeds 

 to consider several of the possible ways in which they may arise. 

 While other theories prove unsatisfactory, he shows by very clear 

 figures that the beams are probably due to an infolding of the 

 radial walls of the cambial cells. Such a fold having been formed, 

 its connection with the radial wall is resorbed and the greater 

 part of the fold remains as a cross-bar, or plate extending from 

 one tangential wall to the other. As the cambial cell divides, the 

 beam-like structure extends through both daughter-cells, and so 

 arise the radial rows of beams. By further resorption the beam 

 in the cambial cell gradually diminishes in size and finally disap- 

 pears, which accounts for the fact that the rows are- not always 

 continuous from wood to bast. In regard to the mechanical rela- 

 tions of the beams, Miiller finds that, during their development, 

 they are stretched, but often at later stages compressed as in the 

 crushing of the bast by the tension of the bark. They then be- 

 come variously curved. Unfortunately no data for determining 

 the physiological significance of these interesting structures have 

 as yet been lound. b. l. r. 



4. Cultures experimentales dans les Alpes et les Pyrenees. (Revue 

 generale de botanique, II, pp. 513-546, pis. 20-22). — In this 

 paper Professor Gaston Bonnier describes an extensive series 

 of alpine cultures, which he has been carrying on for some years. 

 His purpose has been to determine more accurately the influence 

 of altitude upon the characters of different phanerogams, and to 

 observe the limits to which variation due to this cause may ex- 

 tend. In the present communication he describes merely the 

 modifications of the external characters attending growth at high 

 altitudes, and reserves the discussion of the anatomical changes 

 for some future occasion. While his observations concerning the 

 external traits contain little that will be new to anyone familiar 

 with the nature of alpine vegetation, the methods employed in the 

 cultures are very interesting, and might well be applied by 

 American botanists so situated that they can study mountain 

 vegetation. To estimate the modification which is due solely to 

 altitude, it is necessary to remove so far as possible all other 

 differences in the conditions under which cultures of the same 

 species are made. This is not an easy task, but is of course 

 essential to accurate results. No satisfactory conclusions, for 

 instance, could be reached by comparing specimens transplanted 

 to higher or lower altitudes with those growing undisturbed at 



