STRUCTURE, MORPHOLOGY, AND PHYSIOLOGY. 



3 



but to the base of the leaf-sheath ; they are to be 

 found in all grasses (Molinia excepted), at least so 

 long as the internode 

 above has not com- 

 pleted its growth ; but 

 when the base of the 

 internode, the portion 

 which remains longest 

 capable of growth, is 

 transformed into per- 

 manent tissue, one of 

 two things may hap- 

 pen : the tissue of the 

 sheath - node may re- 

 main turgescent and 



Capable of growth, then FlG - *•— -^ Fragment of culm of wheat with 



x . sheath-node, somewhat bent. B, Longitudi- 



no Swelling is formed na ^ section of the same; sk, sheath-node; hb, 



„ . point of insertion of the sheath. C, Andro- 



at the base of the Culm- pogon; the sheath s removed on the left side 



. . in order to show the culm-node, hk ; sk, 



joint ; Or a true Culm- sheath-node. 



node may be developed from one to three millimeters 

 above the sheath-node, assuming all the properties of 

 the sheath-node (see below), and at the same time the 

 latter shrivels up. This last is the case with all Andro- 

 pogonece and Panicece, and many Bambusece, as well as 

 with many single genera of other tribes (for example, 

 Stipa, Eragrostis, Pappophorum, Arundo, etc.). The 

 majority of Agrostidece, Avenece, Festwcece, and Triticece 

 have only sheath-nodes ; and, finally, there are grasses 

 without any distinct nodes, such as have their branches 

 very thickly leaved, from the fact that in these the 

 sheaths of several internodes overlap each other, as in 

 many Bambusece. 



The nodes are not, as is often supposed, to give 

 strength to the culm ; they are composed of a some- 

 what thin-walled parenchyma whose cells are strongly 

 turgescent and through which run delicate fibro- vascular 

 bundles with well-developed bundles of collenchyma on 

 the outside. Their function consists solely in the erec- 

 tion of culms that have become bent down. The paren- 

 chyma of the node is geotropically sensitive, and as 



