34 Macfarlane. — Contributions to the History of 



the bundles also show granules though of smaller size. Large 

 quantities of starch likewise lie in the cells that make up the 

 triangular area between the midrib bundle and its side 

 branches. Very few granules occur in the cells along the 

 sides of the bundle, and practically none in those beneath it. 

 This relation the author has found to remain unchanged in 

 non-secreting leaves even after these have been kept in the 

 dark for several days. If now serial sections be made from 

 the base of the blade down through the narrowed process 

 connecting blade and winged petiole, the transition from the 

 former to the latter is sharply marked by absence of stored 

 starch around the bundle. As stated below, we believe that 

 the starch is largely utilized during contraction and secretion, 

 for then it is replaced in the bast cells by an oil and at the same 

 time it increases greatly in amount in the upper epidermal cells, 

 probably due to transference of the oil to the epidermal cells, 

 and temporary storing of it previous to excretion through the 

 glands. It is specially worthy of note that while surface 

 pieces of epidermis become deep blue from the amount of 

 starch they contain, not a trace of starch can at any time be 

 detected in the gland cells. 



As regards the starting of the closing movement, and 

 the mechanism that effects closure, various views have 

 been advanced. It is generally conceded that after 

 stimulation the protoplasm becomes permeable to the out- 

 ward flow of water, but there are grounds for believ- 

 ing that it is penetrated by minute pores through which 

 the migrating water can escape. It is quite possible 

 that these might exist, though our microscopes or methods 

 of manipulation might be such as to fail in demonstrating 

 them. But in examining various leaf sections very minutely 

 under a one-ninth objective, several of the clear cells 

 were noticed in which the protoplasm showed an evident but 

 extremely fine striation at right angles to the leaf surface. 

 These cells were chiefly noticed in the third and fourth layers 

 beneath the upper epidermis. One must be careful not to 

 confound them with very similar appearances that are shown 

 by the cell walls when these are rather strongly illuminated, 



