394 
Transactions of the Boyal Society of South Africa. 
These contrivances are usually also calculated to reduce transpiration 
very considerably, and their function in this direction is undoubtedly 
of vital importance to the plant, but at the same time the fact that they 
reduce the light has hitherto, as a rule, not received that attention which 
it deserves. A large number of our South African plants, although 
apparently exposed to the fierce rays of the sun, are really physiological 
shade-plants 
Now H. truncata has actually retired into the shade by burying 
itself to a large extent underground, and as the basal part of the leaf 
still acts as an assimilating organ, some provision is necessary for the 
light to reach it at all, and the light can only reach it through the 
" window " which is at the top. It does not require any learned calcula- 
tions to show that the amount of light entering through such a window 
cannot be very great, and, moreover, the window-pane is not quite clear. 
I abstain from making any remarks on other species of Haworthia with 
similar " windows," as I have not observed them amongst their natural 
surroundings,! and have no precise information as to how they grow 
under those conditions, nor can I say anything about the peculiar Bulhine 
mesemhrianthemoides which I have not seen alive. 
* O. V. Derbyshire, in his " Observations on Mamillaria elongata^^ {Annals of Botany, 
xviii., p. 375), concludes that the papillae on some species of Mesembrianthemum, and 
the terminal bristles on others, serve also the purpose of diminishing the light that 
reaches the assimilating tissues. I hope to be able to refer to his conclusions more in 
detail before long, as I am conducting a series of experiments which are calculated to 
throw light on them. In the meantime I should like to state my opinion that they seem 
to me to require clear experimental proof before they can be accepted in their entirety. 
f The whole argument of Berger's that these plants have arrangements which secure 
an improved supply of light, and which do not serve as a protection against intense light, 
appears to me, however, quite wrong without a similar explanation as I have given for 
H. truncata. 
DESCEIPTION OF PLATE. 
Haworthia truncata, Schonl., n. sp. 
FIG. 
1. Whole plant (natural size). 
2. Dorsal view of leaf with tops of roots and base of peduncle (natural size). 
3. Median longitudinal section of leaves and stem. The thick black lines in the leaves 
indicate the extent of the assimilating tissue (natural size). 
4. Two stamens and portion of the corolla (about 3/1). 
5. Gynsecium, &c. (about 3/1). 
6. Young capsule, with corolla still attached (natural size). 
7. Bipe open capsule (natural size). 
