1908.] NATURAL SCIENCES OF PHILADELPHIA. 451 



can^be better used by such branches, to which the moist soil offers at 

 the same time an opportuntity to root. Such plagiotropous stolons 

 with elongated internodes show, however, orthotropous branches, 

 and we, therefore, have on the same shrub branches which react 

 differently to the light, some that are stoloniferous and plagiotropic, 

 others that are leaf-bearing and orthotropic. After a time, however, 

 the bushes assume a different habit by a suppression of parts, so that 

 the older stems show two horizontally directed branches (plagiotropic), 

 which separate from the common stem in a dichotomous manner. 

 Now if we examine figs. 1 and 2 of PI. XXV, we see that all of the lateral 

 spurs that are formed from such a plagiotropic branch are placed on the 

 upper side (orthotropous), where their leaves receive to the best advan- 

 tage the light which filters down through the leafy canopy above. 

 Each segment of such a branch represents a sympodium, where there 

 are a series of phytons placed one after the other in serial order. By 

 this method of sympodial branching, each new branch with the sup- 

 pression of a bud on the other side and torsion of the axis, terminates 

 in a leafy extremity, and the elongation of the branch according to 

 this arrangement depends on a lateral bud (fig. 3). In this case clearly, 

 as all of the leaves are directed dorsiventrally by light relationship, 

 the permanent branching system is determined largely by the influence 

 which the light has had in producing a one-sided growth of the lateral 

 dichotomous branches of the adult plants. The fruit stands vertically 

 above the broad, cordate leaves, as shown in figs. 4 and 5. Attention 

 might be directed in closing to the color change which takes place in 

 the leaves with the approach of autumn. The leaves become bronzed 

 to a greater or less extent. Sometimes the bronze is in the form of 

 blotches. In other leaves one side is bronzed, the other side is green, 

 and in many examples the whole leaf rapidly bronzes. What induces 

 the bronzing of one side of the leaf first, while the other side remains 

 of a bright green color? Is it a light reaction? The photograph in 

 PI. XXIV was taken by Mrs. Harshberger; the drawings reproduced 

 in PI. XXV were made from rough drawings and data furnished Mr. 

 Louis Schmidt by the writer. 



