530 T. Holm — Ceanothus Americanus and ovatus. 



cells are located. A thin-walled endodermis surrounds the 

 central cylinder of leptome, cambium and hadrome, with nar- 

 row medullary rays and a central, solid, starch-bearing pith. 

 Inside the endodermis are furthermore four strands of thick- 

 walled stereome bordering on the leptome and located in the 

 same radius as the innermost four groups of vessels, which 

 represent the proto-hadrome. 



The same structure was dbserved in the epicotyl (Ep. in fig. 1), 

 with the only exception that the stereome does not occur here 

 as four separate strands, but as several, which form a more or 

 less interrupted sheath around the leptome. The other inter- 

 nodes of the seedling possess a collenchymatic cortex (the peri- 

 pheral two or three layers), and the endodermis is more dis- 

 tinctly differentiated, and contains deposits of starch. The 

 stereome forms here an almost completely closed sheath, and 

 druids of calcium -oxalate were noticed in the cortex. These 

 various stem-portions of the seedling are, thus, able to 

 increase in thickness, even if the hypocotyl and, sometimes 

 also, the epicotyl, are the only parts that persist. 



If we now examine the basal portion of a flower-bearing 

 shoot, we notice a corresponding structure, but the various 

 tissues show here a somewhat stronger development. The 

 epidermis is more thick-walled, and the cortex more compact,, 

 with the mucilage-cells wider and longer ; endodermis is thin- 

 walled as in the young specimens, while the stereome }s very 

 thick-walled, forming an almost closed sheath around the cen- 

 tral cylinder. The cambium is more distinct, and the had- 

 rome consists of numerous rows of vessels with the medullary 

 rays broader. 



J he internal structure of the vegetative organs of Ceanothus 

 ovatus. — The root shows the same structure as that of C. Ameri- 

 canus. In regard to the mature leaves, these are almost glab- 

 rous, the hairs being confined to the larger veins on the dorsal 

 face of the blade. The stomata, which are surrounded by four 

 to six cells, are in this species distributed over both faces of the 

 blade, most numerous, however, on the dorsal, and they are 

 raised a little above the surrounding epidermis. The pneu- 

 matic tissue is more compact than observed in the former 

 species but otherwise the structure is identical. 



The petiole shows the same structure as that of C. Ameri- 

 canus, and in regard to the stem, the flower-bearing shoot, we 

 observed no character of any essential importance, by which 

 to distinguish this from the stem of the former species. 

 When compared with each other these two species resemble 

 each other very much from seedling to mature plant. But 

 characteristic of 0. ovatus is, however, the terminal inflores- 

 cences and the narrower leaves with stomata on both faces. 



Brookland, D. 0., July, 1906. 



