The Resin-Canals in the Guayule. 171 



THE CANALS IN THE LEAF. 



Since the canals in the leaves are related only to the primary cortical 

 system, this relation will now be taken up. 



EARLY FOLIAGE LEAVES. 



The above-mentioned pair of primary cortical canals which enter the 

 petioles of the earlier leaves end blindly at different levels in the petioles 

 and in the leaf-blade 1 (plate 38, figs. 3 to 9). The marginal leaf-traces 

 enter the petiole unaccompanied by canals, but arise de novo in the petiole 

 dorsal to the lateral traces. These they follow into the leaf -blade, and 

 branch, constituting a latero-dorsal system. The dorsal system may be 

 entirely absent from the blade (plate 38, fig. 5). There is also a ventral 

 system composed of three canals, one opposite each of three prominent 

 bundles, namely, the median and two lateral. These arise independently 

 and de novo, that opposite the median trace in the petiole, and those oppo- 

 site the lateral ones, in the blade. They originate analogously with the 

 pith-canals, independently of the endodermis 2 (plate 37, figs. 6, 7). 



THE LATER LEAVES. 



The later leaves, in which their definitive character is assumed, re- 

 ceive usually three to five (occasionally six or seven) cortical canals from 

 the stem, one with the median and two with each of the stronger lateral 

 traces (plate 38, figs. 2, 10 to 18). These canals, which enter the blade, 

 follow the traces which constitute its prominent veins. The lateral 

 canals may branch, usually not more than once. Thus the dorsal system 

 of canals has, at most, usually not more than five ducts. The median canal 

 follows the midrib to the apex of the leaf. The lateral ends some distance 

 from the apex. The ventral system arises de novo in the petiole as three 

 to five independent ducts (plate 38, figs. 10 to 13), the median arising first. 

 The lateral canals follow the main limbs of the lateral traces and give off 

 branches to veins of a higher order, until, in a transverse section, there 

 may be five or more on each half of the blade. It is thus seen that the 

 ventral system is peculiar to the leaf and is more extensive than the dorsal 

 system. The canals anastomose in the upper part of the blade and follow 

 the veins. 



PRIMARY CANALS IN BRANCHES. 



The primary system of cortical canals in a branch is derived from two 

 canals on either side of the appropriate leaf-trace. At the level at which the 

 bud appears, the adjacent canals in the chief stem enlarge radially and send 



1 The behavior described is not invariable. One case was found in which 

 only one branch of the canal anastomosis entered the first leaf, while the second 

 leaf was normal, having two canals. The third foliage leaf in this plant also had 

 but one canal. One instance of a leaf at about the twentieth node had two canals. 

 This condition offers an analogy to that in the cotyledons, which may be held, 

 though only tentatively, as speaking for the more primitive character of the 

 double arrangement. 



2 It is worth noting here that there is a single ventral canal opposite the mid- 

 vein in the cotyledon of the common sunflower, Helianthus annuus. 



