T. Holm — Ceanothus Americanus and ovatus. 523 



Art. XLYL — Ceanothus Americanus L. and ovatus Desf. ; 

 a morphological and anatomical study ; by Theo. Holm. 

 (With rive figures in the text, drawn from nature by the 

 author.) 



Ceanothus Americanus L. is very frequent in the vicinity of 

 Washington, D. C, and occurs in dry copses or in open fields ; 

 the other species C. ovatus Desf. is confined to the Potomac 

 shore, where it inhabits the rocks at " Little Falls " associated 

 with Baptisia australis R. Br., Physostegia Virginiana 

 Benth., Lythrum alatum Pursh, Scirpus lineatus Mich'x., etc. 

 They both are widely distributed through the Eastern and 

 Central States extending northward to Canada, while nearly 

 all of the other species of the genus are Calif ornian. 



The Rha??inacew, to which our genus belongs, comprises 

 thirty-seven genera in accordance with Bentham and Hooker ; 

 the diagram of the flower has been described by Eichler,* and 

 the general types of the inflorescence have been briefly men- 

 tioned by the same author (1. c). 



A few species of Rhamnus have been studied at the seed- 

 ling-stage by Irmisch,t and of Colletia by Lubbock.^ Myco- 

 rhizce were detected in Ceanothus Americanus by W. J. Beal§ 

 and the fungus identified by Geo. F. Atkinson as Franhia 

 Ceanothi. \ 



The internal structure seems to be better known and a very 

 instructive discussion of the anatomical features of a number 

 of genera and species is to be found in Solereder's work : Sys- 

 tematische Anatomie der Dicotyledonen.^f 



However, among the Rhamnacew thus treated, Ceanothus 

 has been merely briefly touched upon, and since the writer has 

 had the opportunity of studying the two species that occur in 

 the district of Columbia, the following notes may be presented 

 as a small contribution to the knowledge of the genus. 



The germination. — As stated above, Irmisch has described 

 the seedlings of Rhamnus cathartica and Rh. Frangula (1. c), 

 and he calls attention to the fact that the cotyledons of the 

 former are epigeic, but of the latter hypogeic. In Rh. 

 cathartica the cotyledons are green, larger than the succeed- 

 ing leaves during the first season, and borne upon a distinct 

 hypocotyl. The leaves succeeding the cotyledons are arranged 



* Bltithendiagramme. Pars 2, 1878, p. 371. 

 f Flora, 1855, p. 625. 



\ A contribution to our knowledge of seedlings. London, 1892, vol. i, 

 p. 344. 



§ Botan. Gazette, vol. xv, p. 232. 



f Bull. Torrey Bot. Club, vol. xix, 1892, p. 171. 



^[Stuttgart, 1899, p. 247. 



