iqi2] JONES— DIANTHERA 27 



is needed, however, especially to find out if possible the physiologi- 

 cal value of the endodermis. Possibly such work would lead to 

 the discovery of the reason why some species of this genus are 

 monostelic, and apparently normal in every way, while other 

 species are abnormal in beine astelic, and in Dossessine medullarv 



vascular tissue. 



Summary 



The mature plant of Dianthera americana is astelic, instead 

 of polystelic, as claimed by Holm. It possesses six peripheral 

 meristeles and one central medullary bundle, each completely sur- 

 rounded by an endodermal sheath. At the nodes these anastomose. 



The seedling is at first monostelic; the individual bundles 

 gradually become surrounded by the endodermal sheaths. 



The mature type of structure with six bundles is derived from 

 the seedling type with only four, by the increase of the size of the 



leaf 



gaps. 



The inflorescence axis is monostelic. 



Dianthera americana differs from related forms in the lack of 

 interfascicular cambium, the individual bundles becoming sur- 

 rounded by endodermis. Its medullary bundle is quite com- 

 parable to the medullary bundles of Acanthus spinosus, many 

 Campanulaceae, and other plants. 



It is probable that astely is merely a phase of monostely, the 



endodermis being a physiological layer, the medullary and cortical 



parenchyma becoming similar owing to like physiological conditions. 



Astely in this plant is probably correlated with its aquatic 

 habitat. 



Johns Hopkins University 



Baltimore, Md. 



LITERATURE CITED 



• <-ol, A., Relation des faisceaux medullaires avec les faisceaux normaux. 

 Journ. Botanique 16:234. 1902. 



2. 



1 Recherches sur la disposition des faisceaux dans la tige et les 

 feuUles de quelques dicotyledones. Ann. Sci. Nat. Bot. VIII. 20: 1. 1904. 



3- -DeBary, A., A comparative anatomy of the phanerogams and ferns. 

 English translation. Oxford. 1884. 



4. Gregoire, V., La valeur de la couche amylifere dans la tige, et la theorie 

 stelaire de Van Tieghem. Ann. Soc. Sci. Bruxelles 34:5-12. 1910. 



