554 DE. A. J. EWART ON ASSIMILATORY INHIBITION. 
Crassula. In Engler and Prantl’s ‘ Natürliche Pflanzenfamilien,’ 
iii. 2te Abt. p. 37, I united Tillea, Linn., Bulliarda, DC., Helo- 
phytum, Eckl. & Zeyh., and Combesia, A. Rich., with Crassula, 
and placed them all under the section Zillea; and it seems to 
me that I was quite right in not considering the possession of 
tetramerous flowers to be of generic importance, especially as I 
have since found tetramerous flowers in a number of species 
of Crassula—e. g., they are of common occurrence in C. spathu- 
lata, Thunb., and C. expansa, Ait., and are the rule in C. multicava, 
Lem. (=C. quadrifida, Baker). Thus I have no hesitation in 
placing C. Marlothii also under the section Zillæa as defined in 
the * Natürliche Pflanzenfamilien.’ 
Further Observations upon Assimilatory Inhibition. By ALFRED 
J. Ewart, B.Sc., Ph.D.; 1851 Exhibition Scholar. (Com- 
municated by Prof. R. J. Harvey Gizson, F.L.S.) 
[Read 17th December, 1896.] 
IN a previous paper an account has been given of the various 
modes in which an inhibition of assimilation may be induced 
experimentaly. The following paper gives the effects of the 
continued absence of light or of CO, upon assimilation, which in 
the previous works were not mentioned. 
The most obvious effect of the absence of light is that the 
chlorophyll grains do not become green but contain a yellow 
pigment, etiolin. Draper* in 1878 stated that etiolated plants 
in light can evolve oxygen; and Engelmann t found later, by 
means of the Bacterium method, that the etiolated leaves of 
seedlings of Nasturtium show a distinct power of assimilation. 
These results have not, however, been generally accepted as 
forming a complete proof that etiolin can take the place of 
chlorophyll as an assimilatory pigment, and have been by some 
botanists met with flat denial Thus Timiriajeff f. objects 
entirely to the Bacterium method, as the absorption of heat-rays 
* Draper, Scientifie Memoirs, 1878. 
t T. W. Engelmann, Bot. Zeitg. 1881, p. 445. 
t C. Timiriajeff, “ Sur la Fonction chlorophyllienne," Ann. Sci. Nat. 7 sér. ii. 
1885, p. 99 
