134 STUDIES IN ELECTRO-PHYSIOLOGY: 



quantity, protection of a similar nature is afforded by resin, 

 or by a covering or capsule of a fibrous character, as, for 

 instance, in the leaf of the ivy and the capsules of various 

 beans and seeds, etc. 



In regard to the comparison by Sachs of the laticiferous 

 vessels of plants to blood-vessels of vertebrate animals, he 

 instanced the fact that when a milky stem is cut not only 

 the low cut surface of the apical portion but the upper one 

 of the root-stock also extrudes the latex. Besides, the 

 laticiferous vessels are extremely narrow capillary tubes, 

 the normal terminations of which in the buds, leaves, and 

 root-apices are closed. How, he asked, could fluid flow 

 out at all on cutting such capillaries closed at the ends 

 unless the fluid was under pressure ? " When we wound 



Fig. 69. Fig. 70. 



Cells from the leaf of Elodea ; Two cells from a staminal hair 



p, protoplasm. of Tradescantia. 



ourselves the blood does not simply flow out, it is driven 

 out." 



