ORR—AESCHYNANTHUS CHORISEPALA. 225 
of the internal tissues, and their partial disorganisation follows, 
but the structure of the epidermal layer enables the plant to 
minimise the effects of such an accident. The epidermal cells 
have their outer and lateral walls thickened, while the inner 
walls remain unthickened, and the whole layer thus closely 
resembles the annulus of a fern sporangium, but in an inverse 
manner. When these cells lose their water, the broken ends of 
the layer curve naturally inwards, and enclose, and protect the 
exposed underlying tissue. As disorganisation proceeds, from 
below -upwards, ultimately only the outer layer of the upper 
epidermis remains, stretched across the fissure. With the 
gradual increase in tension this layer also ruptures, and, as it is 
similar in structure to the lower epidermis, its behaviour, as it 
loses moisture, is identical. The ruptured parts curve inwards, 
and become closely applied to the outer side of the inrolled 
lower epidermis. In this way the wound is sealed by a double 
layer of thick-walled cells, and the internal tissues are protected 
from further injury. 
