436 



significance. In January, 1879, I observed specimens of Cassia tomentosa 

 in a hothouse. I found the edges of leaflets on young shoots were curled 

 under. This curling seemed to be due to the increased growth of the upper 

 side, which showed a pustule-like convexity. When these convexities were 

 fewer and located along the mid-rib, the leaflet was less curled. If they 

 were scattered abundantly and uniformly over the whole surface, the leaf 

 seemed almost blistered. This cannot be said to be actually blistered, how- 

 ever, because the convexity of the upper side corresponds to no e(|ually 

 great concavity of the underside. 



The swelling is conical, having, at first, the same color and dull upper 

 surface as the rest of the leaf. Later the tip of the cone becomes light 

 colored, more rigid and shiny. Still later the tip becomes yellow, broadens 

 and finally ruptures (Fig. 75, ^e), if the whole leaflet has not already turned 



Fig. 75. lioaf intumescences in Cassia tomentosa. (')rig.) 



yellow, the swelling now seems depressed in the centre, tunnel-like, and 

 turns brown. 



The phenomenon is due to a sporadic tube-like outgrowth of the upi)er 

 palisade parenchyma (p). The inner side contains many chloroplasts closely 

 packed together and, toward the spongy parenchyma, is provided with 

 slender, slit-like intercellular spaces filled with air. 



With the appearance of swelling, the chloroplasts begin to disappear 

 from the tip of the cell backward, a few of the cells become elongated ; 

 gradually the surrounding tissues are involved. More and more chlorophyll 

 is dissolved as the elongation advances, so that finally the palisade cells, 

 which have become tube-like, seem almost entirely colorless or are provided 

 with a few small yellowish grains scattered throughout the whole cell lumen. 

 With this elongation of the cells forcing up the epidermis there is a slight in- 

 crease in width, which presses the cells ver}' close against one another 

 laterally, with only small intercellular spaces in the spongy parenchyma. As 



