86 CARNEGIE INSTITUTION OF WASHINGTON. 



monograph. Dr. Britton carried out field investigations on the Isle of 

 Pines and in northern Cuba during the early part of the year, and Dr. 

 Rose intends to visit the northern coast of Venezuela in the autumn. 



The first volume of the monograph will include descriptions and 

 illustrations of the two tribes Pereskiea) and Opuntiese. It is expected 

 that the second volume, the Cerea3, will include descrii)tions and illus- 

 trations of the two subtribes Cereanse and HylocereaniB ; the third is 

 designed to include the thi'ee subtribes, Echinocereanse, Echinocactanse, 

 and Cactanse, while the fourth will probably comprise the three sub- 

 tribes CorjTDhanthanai, Epiphyllanse, and Rhipsalidana?. Manuscript 

 and illustrations for all the volumes are largely prepared. 



If expeditions to Venezuela and to Paraguay, southern Brazil, and 

 northern Argentina are successfully carried out, the only extensive 

 cactus region little known to us will be that of Ecuador. 



Improvement of Guayule, the Desert Rubber Plant, by W. B. MacCallum. 



Much of the interest in the desert rubber plant, Parthenium argen- 

 latum, has centered at the Desert Laboratory since the pubhcation by 

 the Institution of Professor F. E. Lloyd's book on this wild plant. 

 The volume in question,^ Guayule : A Rubber Plant of the Chihuahuan 

 Desert, embodies the results of an organized attempt to bring under 

 cultivation a hitherto feral desert plant, together with an extensive 

 ecological study of the same under normal and cultural conditions. 

 Careful consideration is given to the question of rate of growth and 

 reproduction of the guayule in its native habitat, and a large body 

 of pertinent data is given. The various conditions of climate, soil, 

 vegetational environment, and parasitism affecting the plant are pre- 

 sented in this connection. The life-history, habit, and anatomical and 

 histological structure of the wild and cultivated forms are minutely 

 described and compared, in order to secure exact knowledge concerning 

 the relation between growth and the rate of rubber secretion. 



The wild shnibs are collected in great quantities in Mexico and the 

 rubber, which grades much lower than Para, is extracted by such 

 simple processes as to make it a very profitable operation. The task 

 of developing methods of cultivation has now been successfully accom- 

 pHshed by Dr. W. B. MacCallum and in making a genetic analysis 

 of the plant he has established the fact that it includes a large number 

 of elementary species which do not readily interbreed. 



The company under whose auspices the experiments in cultivation 

 were carried out has purchased 7,000 acres near Tucson, and guayule 

 is now being established on this land. This effort is notable in that it 

 is a successful attempt to bring a wild plant under profitable cultiva- 

 tion, and that it is the only rubber-producing plant within the borders 

 of the United States. 



'Carnegie Inst. Wash. Pub. No. VAO, viii4-213 pp., 46 pis., 20 figs. 



