84 



COMPENDIUM OF GENERAL BOTANY. 



plane ; those bundles placed in a somewhat more lateral position 

 penetrate less deeply and describe a smaller curve ; those still more 

 lateral enter least deeply and soon extend vertically downward. 

 In monocotyledons the course of the vascular bundles in the tan- 

 gential plane may be described as follows : Each radially curved 

 hundle inclines in a tangential direction. Among dicotyledons a 

 tangentially inclined course of the vascular bundles is the rule ; 

 they unite laterally after they have taken an isolated course down- 

 ward for some distance. Fig. 48 represents the tangentially in- 

 clining course of the leaf-bundles of Sedum refiexwin (dicotyledon) 

 upon the surface of a cylinder. 



There is a leaf at every node and every leaf contains vascular 

 bundles. The radially diagonal course 

 of the vascular bundles in monocotyle- 

 dons is shown in Fig. 49, which is a dia- 

 gramatic median longitudinal section. 

 Only a few of the leaf-bundles are rep- 

 resented in order to illustrate the rela- 

 tions explained above. The dotted lines 

 are intended to show the tangentially 

 inclined course of the radially curved 

 bundles. The arrangement and distri- 

 bution of vascular bundles, according to 

 the requirements of nutrition, that is, 

 for the uniform distribution of water 

 and of food- substances, have received 

 special attention from Habeelandt. ' 

 The numerous anastomoses of vascular 

 bundles in \\\q, leaves are of great im- 

 portance in cases of local injury, in that 

 the neighboring bundles are thereby en- 

 FiG. 49. abled to take up the work of those de- 



stroyed. (Tlie circulatory system in man is similarly arranged.) 



The following is of importance in regard to the arrangement 

 and structure of the vascular bundles in the leaA)es. Green leaves 

 are for the purpose of assimilation. Therefore the mechanical 

 elements must maintain these flattened organs in a suitable position 

 with regard to the light (see pp. 67 and 68 in regard to the 

 ' PKys. Pflanzen-Anatomie. 



