T. Holm — Ceanothus Americanus and ovatus. 527 



tion, and that is the purely vegetative nature of the terminal 

 bud in G Americanus in contrast to G. ovatus, where the 

 branches are terminated by an inflorescence. In G Americanus 

 it seems to be a constant character that the inflorescences are 

 lateral ; the terminal vegetative bud does not, however, seem 

 to be of any importance to the plant, since the shoots die off 

 to near the ground as observed in the younger specimens. In 

 G. ovatus we observed no case where the apical inflorescence 

 was not terminal, but it was frequently noticed, however, that 

 the branches bore lateral inflorescences below the terminal ; thus 

 two or three inflorescences may be developed on the same 

 shoot. We regret to say that the herbarium material which 

 we have examined of the other species was not sufficient to 

 demonstrate whether the apical vegetative or apical floral bud 

 is the one that is most characteristic of the genus. Besides 

 the lateral floral branches in G. Americanus, we noticed also 

 that lateral vegetative shoots may be developed below these ; 

 in many cases the first two leaves of these vegetative shoots 

 were observed to be opposite, similar to those of the seedling. 



In regard to the inflorescence, the flowers are arranged in 

 small helicoid cymes, destitute of fore-leaves. 



If we compare now the seedling of G. ovatus with that of 

 O. Americanus, described above, we find the same structure, 

 the epigeic cotyledons, the distinct hypocotyl and the two 

 opposite leaves preceding the spirally arranged. The primary 

 root shows the same development, but we were unable to detect 

 the mycorhizse ; these were evidently broken off since the 

 roots were more or less damaged by being dug out of the 

 stony soil. The growth of the shoots in mature specimens is 

 identical with that of the former species with the exception of 

 the inflorescence being terminal. 



The internal structure of the vegetative organs of Ceanothus 



Americanus. 



The root. — During the first season the root has already com- 

 menced to increase in thickness, but the epidermis is still pre- 

 served, and bears numerous hairs. No exodermis is differen- 

 tiated, and the cortical parenchyma consists only of five 

 compact strata. The endodermis is thin-walled and surrounds 

 a pericambium and several groups of leptome separated from 

 the haclromatic rays by layers of cambium. No hyphae and 

 no mucilage-cells were observed. In the second year the root 

 has become somewhat compressed near the base ; epidermis 

 lias been thrown off, and a secondary cortex of about six com- 

 pact layers has been developed. The central cylinder shows 

 the irregular increase in thickness as described above, due to 

 the one-sided growth of the hadromatic rays. Near the apex 

 of the same root the structure is normal with the various ele- 

 ments arranged strictly concentric. The mycorhizse appear as 



