i 9 1 2] JONES— DI AN TH ERA 25 



generate du corps qui ne se separe pas alors en ecorce et conjonctif" 



(P- 2 75)- 



Strasburger (9) distinguishes between the inner layer of the 



which is a morphological laver. and the endodermis 



m 



of water through its cells. Such a layer is found in a position to 

 shut off the water-conducting system of a plant from its air- 



* 



containing lacunar system, but this position may vary within the 

 same genus, and has no necessary connection with any morphologi- 

 cal region" (quotation from Tansley io). 



According to this interpretation of the endodermis, which is 

 therefore merely a physiological layer, astely is merely a modifica- 

 tion of monostely. This is the view already taken by Strasburger 

 (9) ; the same idea is presented in a recent paper by Gregoire (4). 

 The parenchyma of the central cylinder, that is, outside of the 

 endodermis, becomes different from that inclosed within the sheath, 

 owing to the different physiological environment, and it becomes, 

 like the cortical tissue, a response to the same physiological 

 conditions. 



If we leave out of account for the present the surrounding endo- 

 dermis, we see that the medullary system of Dianthera americana 

 corresponds to what Col (i), in his work on the arrangement of 

 bundles, calls "serie M\" He defines this type as follows 

 2 42): "faisceaux normaux rentrant dans la moelle de la tige. lis 

 s accolent inferieurement a d'autres faisceaux medullaires, et tous 

 ceux des entre-noeuds les plus inferieure de la tige se poursuivent 



et se terminent isolement dans la racine (dans le bois) ou a la base 

 de la tige." 



Weiss (14) has shown that all medullary bundles of the stem 



are foliar bundles. The work of Lignier (7), Kruch (6), and Col 



V 1 * 2) fully confirms this. In Dianthera americana it is easy to 



follow the leaf trace downward through two internodes, and to see 



that a part then turns inward to form the medullary vascular 

 tissue. 



In a paper describing for the first time the medullary bundles of 

 Acanthus spinosus, Vesque (13) says that he thinks the primary 

 effect of the internal position of the phloem is its very efficacious 



