8 ON THE GREEN COLOUR OF THE HAIR OF SLOTHS. 
tissues. But the spread of an epidermis from the margin of the 
wound, which oecurs in animal tissues in the process of scabbing, 
does not take place in plants. No such lateral growth is obser- 
vable after a partial removal of epidermis, whether the parts be 
left unprotected or kept beneath a bell-jar in an atmosphere satu- 
rated with moisture. In the latter case the cells exposed may 
preserve their vitality. After the removal of epidermis from the 
leaves of the Hyacinth, I have seen some of the denuded vertical 
cells elongated and club-shaped, as after partial section of the 
peduncle. 
In Agave a many-layered covering of cork is produced on that 
portion of a leaf from which the original epidermis has been re- 
moved; and the same is true of succulent leaves, the repair being 
the same as that set up after the injury of an amputation. 
On the Green Colour of the Hair of Sloths. 
By H. C. Sogpy, LL.D., F.R.S., F.L.S., Vice-Pres. Geol. Soc. 
[Read April 7, 1881. Abstract.] 
Turis paper in full, with a woodcut, will appear in the Society's 
Journal of Zoology, No. 87, vol. xv. p. 337. Ostensibly connected 
with a vegetable parasitic growth, the author has nevertheless 
treated the subject rather from a zoological point of view, or with 
more prominent bearings in that direction. 
Dr. Seemann, in a letter quoted by Dr. J. Edw. Gray (Proc. 
Zool. Soc. 1871, p. 428), raised the question whether the green 
tint of the hair in certain species of Sloths might not be due to 
a parasitic Alga. The subject received no further attention in 
England, though it seems Weleker and Kühn had already pub- 
lished a memoir thereon in * Abhand. der naturf. Ges. zu Halle? 
in 1866 (vol. ix. p. 20). 
Mr. Sorby, with the advantage of studying fresh material (from 
theliving animal) and not dried hairs (as had previous observers) of 
several species of Sloths, corroborates in a great measure Welcker 
and Kühn's observations. He enters into the structure and 
makes comparisons with the hair of several mammals; and thus ` 
shows that the hair of Cholopus differs in several particulars, and 
that the growth of the green Alga is most unmistakably related 
to this aberrant structure. 
Welcker and Kühn found a difference in the parasitic plants 
