THE PLANT WORLD 



251 



Plants of this group are almost entirely dormant during the season 

 unfavorable for growth, and produce a rosette of leaves with a shoot of 

 greater or less extension on which are borne the flowers during the rainy 

 or favorable season. IJmonuim limbatum Small, which has recently come 

 under the notice of the author, may serve as an example. This plant 

 seems to be known only from near the White Sands in the Tularosa 

 Desert in New Mexico, and during February of this year the numerous 

 shallow " washes " that extend across the arid plain west of Alamagordo 

 were seen to bear many thousands of the short stems of these plants 

 bearing the grayish-brown scales and dead leaves of the previous season 

 and having every appearance of being lifeless. When specimens of this 

 kind were brought under suitable cultural conditions and supplied with 

 water an irregular open cluster of elongated leaves was formed, from one 

 of the axils of which a widely branching inflorescence arose that reached 

 a height of 70 cm and bore numerous flowers. The maturation of the seeds 

 was soon followed by the death of the aerial shoot and basal leaves, the plant 

 quickly resuming the inert appearance of the previous season. (Fig. 1.) 



III. Perennial shrubs or 

 trees which bear deciduous 

 leaves. — The leaves are 

 formed during the rainy 

 season or under favorable 

 conditions of temperature 

 and are discarded during 

 the periods of most intense 

 aridity. As a compensa- 

 tion for the comparatively 

 brief season during which 

 the plant has the benefit of 

 the photosynthetic activity 

 of the leaves the stems are 

 are generally rich in chloro- 

 phyl and carry on a limited 

 amount of this work during 

 the greater part of the year. 

 This is still further supple- 

 mented by the petioles and 

 midribs of some species 

 which are retained while 

 the leaflets are discarded, 

 as may be seen in some of 



Fig. I. fJmonhim limbalum SmzU. After a photograph of a the LcgUminOSaC. Ipomoea 

 plant from White Sands, N. M., cultivated in the New , , , 



York Botanical Garden. aroorescetis, the tree morn- 



