236 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



profitable to consider the development of the entire shoot of suc- 

 culents at the same time. The species which might be included 

 under this head, that were used in my experiments comprise, Ag'ave 

 Americana (p. 37), Gasteria disticha (p. 109), Ofiintia Opuntia (p. 

 131), and Dozuiea voliihilis (p. 82) might also be considered here, 

 since its main axis consists of a succulent bulb imbedded in the upper 

 layer of the substratum from, which arises a slender inflorescence 

 axis. The short thick stems of Agave which are completely sheathed 

 by the bases of the fleshy leaves are not excessively elongated in 

 darkness, the only reaction being shown by the leaves. Leaves 

 partially developed when the specimens were placed in the dark 

 room continued elongation, the newer basal portion being chloro- 

 phylless and yellow. The apical parts of such leaves maintained 

 their original green color with but little change in the chlorophyl 

 during periods as long as eight months. Leaves which were devel- 

 oped after etiolation of the plant had begun did not attain dimensions 

 more than half of the normal, and were completely devoid of color, 

 and showed a reduction of the marginal teeth and of other anatomical 

 features. Stems of Gasteria disticha are usually .very short, and are 

 completely sheathed by the ba&es of the fleshy leaves, which are 

 nearly double the length of the stem. During etiolation the stem 

 elongates excessively by an increased growth of about the normal 

 number of internodes, and the upper end of every internode becomes 

 exposed and free from the sheathing leaf-base. The etiolated inter- 

 nodes were distinctly more slender than the normal. Still more 

 attenuation was observed in lateral branches which are usually 

 diagetropic and serve as propagating bodies. In etiolation these 

 were erect and very slender, with internodes much elongated. 

 Opuntia developed cylindrical stems with internodes slightly longer 

 than in the normal flattened structures characteristic of this plant. 

 The etiolated portions endured confinement to darkness for several 

 months but were not so hardy as the normal stems, a fact probably 

 due in part to the extremely delicate outer membrane which failed to 

 protect the underl3'ing tissues from mechanical damage in handling. 

 The reduction of the transpiratory organs, and the comparatively 

 moist air of the experimental chamber in which the plants were con- 

 fined in darkness must also have contributed to the early demise of 

 the etiolated specimens. Bowiea developed short thick inflorescence 

 axes in darkness, with leaves slightly increased in size. 



