46 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



a period of leisure from field observations in a careful study of all the 

 available material at his command relating to this particular genus, and 

 the condensed results of the same are herewith presented. In realizing 

 (perhaps for the first time) the care and labor involved in such an in- 

 vestigation, it has served at least to heighten the respect and reverence 

 due to those masters of botanical science who have taken upon their 

 broad shoulders the burden of a systematic arrangement of the whole 

 vegetable kingdom. 



GENERAL OBSERVATIONS. 



In common with other closely allied genera of EriogoncB, the genus 

 Chorizanthe is readily distinguished in its usual low-branched or decum- 

 bent habit, its clustered radical leaves (which soon disappear with the 

 dry season), from the crown or axils of which spring jointed stems, 

 which are dichtomously branched above, forming a more or less spread- 

 ing summit. In the axils of each joint, subtended by cauline leaves, 

 or more usually reduced to awn-tipped or trifid bracts, there is a closely 

 sessile involucre, the lowest of which, being the first developed, is not 

 unfrequently different in texture and form from the upper ones, which 

 continue the determinate centrifugal inflorescence. By the side of 

 these lower developed involucres spring the branches, single or in 

 pairs, that make up the continued growth. In nearly all cases 

 each involucre is subtended by a pair of opposite or single bracts, 

 which are usually less conspicuous where the involucres are cymosely 

 clustered. In a few cases (C Spinosa), a cluster of less developed and 

 deciduous involucres occupies the larger axils, being quite different in 

 size and appearance from the single central one. With considerable 

 difference in shape and texture, there is still quite a uniformity in the 

 general character of the involucres, all being closely sessile, more or 

 less sharply ribbed, and cleft into three to six divisions terminated by 

 awns, usually recurved and uncinate, or more rarely slightly divergent, 

 and straight. The first in the series, being taken for the type (C Thur- 

 beri), is strongly suggestive of Oxytheca, the genus immediately preced- 

 ing it. It agrees closely in its general habit of growth, its chartaceous 

 involucres, with teeth terminating in straight awns, and its pedicellate 

 flowers, usually two. The singular saccate spurs at the base of the in- 

 volucre cannot be regarded as of any special significance, being simply 

 a contrivance for facilitating its dispersion, which is much more effectu- 

 ally carried out in the succeeding species {C. leptoceras) with an in- 

 creased number of spurs, strongly divaricate, and sharply hooked at 



