942 REV. G. HENSLOW ON THE ORIGIN OF PLANT-STRUCTURES 
Cerastium Boissieri, which is white and tomentose at the summit 
of Ait-Ouabau, became glabrous and of a beautiful green at 
Algiers. 
Hairiness is well known to be a most variable character, and 
although it is recognized as specific when constant and abundant, 
as in Verbascum, and therefore less variable, it obviously becomes 
much less important when it fluctuates. 
It may be observed here that the hairiness as an hereditary 
character varies greatly. Thus, M. Battandier found that 
Bellis atlantica varied when transplanted, yet when raised by 
seed in Algeria did not show similar modifications ; similarly 
Allium Chamemoly, though it was less villous, remained more 
hairy than its congener after cultivation as well as by sowing. 
On the other hand, seedlings of Pastinaca sativa raised in a 
prepared border in the botanic gardens of the Cirencester Agri- 
cultural College became less and less hairy, and finally quite 
glabrous*. 
As a spontaneous variety, Malva parviflora may be mentioned ; 
as grown in the Nile Valley as a culinary vegetable it is not very 
hairy, the hairs being stellate, having only a few rays, sometimes 
two only. As a desert plant, where it appears as a small annual 
for a few weeks only, the stellate hairs increase their number of 
rays. Similarly Hrodium laciniatum is much less hairy when 
growing in waste ground on Rhoda Island in the Nile by Cairo 
than when in the desert. I find that the main differences 
between the two forms may be summed up as follows :—Hypo- 
dermic collenchyma is much thicker in the petiole of the desert 
form. The upper epidermis has its cells similar in size but with 
more hairs. The lower epidermis has cells which are much 
smaller than those of the Nile Valley form. The palisade, 
consisting of two rows of cells, is identical in both cases below 
the upper epidermis; but while there is a lax mesophyll of 
rounded cells on the lower side in the Nile Valley form, the 
corresponding cells are somewhat elongated in shape, thus tending 
to assume the palisadic type characteristic of the lower side as 
well as of the upper in the desert furm. Hairs of the latter are 
more numerous in the proportion of 24 to 10 for the same area. 
Stomata.—These structures are frequently sunk below the 
* Prof. Buckman raised the “domesticated ” variety alluded to in 1847, 
which he called the “Student.” It is still regarded as the “ best variety ” in 
cultivation, according to Messrs. Sutton & Sons of Reading (1894). 
