196 BEwsS—A CAVITY FILLED WITH HAIRS IN 
fundamentally related to selerenchymatous fibres in every respect, 
and are only special cases of the latter, distinguished by their 
form and distribution. 
It is at once obvious that the hairs in this hair-cavity cannot 
be called “ Internal Hairs,” according to De Bary’s description of 
such. 
I have already said that the whole surface of the plant is 
covered with hairs, These hairs on the outside of the stem are 
also of the two kinds, pluricellular and glandular (Fig. 4). 
They are absolutely identical in appearance with the hairs that 
fill the cavity. The pluricellular are again the more numerous, 
and the proportion of glandular to pluricellular is the same as in 
the hair-cavity. 
The cells surrounding the cavity are exactly like the cells of 
the epidermis. ; 
These facts point to the conclusion that we have here an 
internal epidermal structure. 
It is not exactly the case, however, that the cells surrounding 
the central hollow, in response to an air-environment, have 
started to produce an epidermis with hairs. Such would doubt- 
less be a likely and natural explanation, if it were not for the way 
in which the hair-cavity arises. 
Wounding the surface of a stem has been said to cause an 
internal epidermis to be produced, but I hardly think that any 
wound on the surface would cause such a structure as this to 
arise. And, as far as I could see, there was no wound on the 
surface of the stem. ’ 
Another attempt at an explanation is that this might be an 
infolding of the epidermis, the infolded loop, as it were, being 
cut off and forming the cavity. But looking again to the 
method in which it arises, this explanation seems impossible. 
No disarrangement of the vascular bundles, nor any other 
= regularity in the appearance of the stem or distribution of the 
— is apparent, and a vascular bundle lies directly between 
the point where the hair-cavity begins and the outside of the stem. 
- The most natural explanation— which, however, is by no 
means a complete one—is that certain cells in the interior of this 
plant have taken on themselves the character of meristem and 
have laid down an epidermis. 
