DEPARTMENT OE BOTANICAL RESEARCH. 6l 



Variations of Succulents in Volume in Response to Changes in Tempera- 

 ture and Water Supply. — Mrs. E. S. Spalding has continued the series of 

 measurements of the saguaro (Cereus gigantcus) and prickly pear (Opuntia 

 sp.) and now has on hand the accumulated data obtained by the work of four 

 years. Both of the forms exhibit a rapid and marked response by alterations 

 in volume to increase or decrease of the available water in the soil and to 

 loss by transpiration. The flowers of the saguaro show a rate of transpira- 

 tion much greater than that of any other organ yet examined. The fluted 

 columns of the saguaro also undergo marked mechanical adjustments in 

 response to changes in temperature, and the place of origin of the flower- 

 buds seems to be determined directly by the degree of insolation. It is now 

 possible to express all of the alterations and responses in quantitative form. 



The Topography of Chlorophyll Apparatus. — Dr. W. A. Cannon has con- 

 cluded his anatomical studies on the distribution of chlorophyll in the shoots 

 of desert plants, the principal results being embodied in a paper which will 

 soon be published. 



Contrary to the conclusion reached in the earlier stage of the work, it has 

 been established that the depth in the body of the plant at which chlorophyll 

 may persist depends upon aeration and was found to be 6.6 mm. in Cereus 

 giganteiis. The chlorophyll formed in young stems of Cereus, Fouquieria, 

 Krameria, Parkinsonia, and probably Zizyphys persists through the life of 

 the plant, while the layer bearing this substance is usually cut off by the 

 formation of cork. The plants studied may be divided into two groups with 

 regard to foliar habits. In one class leaves are rudimentary or wanting; 

 in the other, leaves are formed and retained during the season when the 

 water supply is greatest. The differences in leaf-habit are accompanied by 

 fairly consistent morphological characters in the stems. Plants with reduced 

 leaf surfaces or with no leaves have palisade parenchyma in the cortex of 

 the stems, and this chlorophyll-bearing layer lies near the surface, with no 

 especially developed protective devices in the epidermal tissues. Species 

 with some leaf surface, on the other hand, have only a spongy parenchyma 

 containing chlorophyll in the cortex of the stems, which is more deeply 

 placed than palisaded tissues in plants devoid of leaves. The tissues ex- 

 ternal to such chlorophyllaceous tissues usually show some protective devices. 



Root-habits. — The study of root-habits, made by Dr. Cannon, has been ex- 

 tended to include a large number of cacti, and it appears that none of this 

 group shows deeply penetrating roots. Many species show a profuse rami- 

 fication immediately underneath the surface, while a maximum depth of 20 

 inches was found in Cereus giganteus. 



With the exception of the juvenile storage organs on the roots of Opuntia 

 versicolor and the thickened roots of Opuntia arhiiscula, these organs are 

 generally slender among the cacti examined. 



