RESPONSE OF EPITHELIUM AND GLANDS 



313 



from the top to the bottom, at the point where the peduncle 

 rises from the bulb, we shall find that the epithelial layer of 

 the upper end passes imperceptibly into a markedly secret- 

 ng (glandular ?) layer at the lower. By this, secretion is 

 constantly taking place, filling up the hollow tube with fluid. 

 In one instance which I measured, the amount of this 

 secretion was as much as 10 grammes in the course of the 

 day. These secreting cells in this, which may be called the 

 glanduloid layer, are very thin- 

 walled and excessively turgid, 

 and, from an evolutionary point 

 of view, these gradual transitions 

 from epidermal to epithelial, and 

 from epithelial to secretory layers, 

 observed under conditions of such 

 great simplicity, are extremely 

 interesting. 



When we come to test the 

 electrical reactions of these tissues, 

 we find, on making electrical con- 

 nections with the external epi- 

 dermis and the internal epithelium, 

 that a natural current flows in the 

 tissue from the external surface 

 to the internal. This would indi- 

 cate that the internal was the 

 more excitable of the two. This 

 conclusion is confirmed on the 



FIG. 192. Transverse Section of 

 tissue of Hollow Peduncle of 

 Uriclis Lily 



Cells of epidermis are small and 

 thick-walled, those of inner 

 surface large and thin-walled. 



application of simultaneous excitation to outer and inner ; 

 for the direction of the responsive current is found to be from 

 the internal surface to the external. 



If, next, electrical connections be made with the epidermal 

 and secretory layers, a current of rest is once more observed 

 from the external to the internal. On excitation, a very 

 strong electrical response is given, its direction being from 

 the highly excitable secreting layer to the less excitable 

 epidermal. From these experiments we see that the 



