MATERIAL FOR STUDY OF LEAF ANATOMY 125 



walled. IStomata are more abundant in this layer of the lamina, 

 a connnon situation in many angiosperms. "IStalked" stomata 

 are frequently present in the midrib region. Multicellular capi- 

 tate halt's, lying within shallow depressions, are relatively com- 

 mon and consist of a terminal group of densely protoplasmic 

 secretory cells (with rather thick outer walls) which are seated 

 upon a small unicellular stalk. Haberlandt (p. 240 ) suggests that 

 the capitate hairs of Syringa may absorb thin films of water from 

 the leaf surface but this supposed function requires further in- 

 vestigation. 



(b) The mcsophyll. This tissue region is composed of two 

 types of parenchyma, viz.: (1) the palisade parenckyma which 

 is found directly beneath the adaxial epidermis and consists of 

 rather narrow, thin-walled, somewhat "rectangular" cells, the 

 long axes of which are perpendicular to the epidermis. Notice 

 that intercellular air spaces are prominently developed in the 

 palisade parenchyma. In addition to a prominent nucleus, each 

 palisade parenchyma cell contains a large number of peripheral 

 cJiloroplasts in which the process of photosynthesis is carried on. 

 Directly internal to the abaxial epidermis occurs (2) the spongy 

 parc7ichyma which is composed of thin-walled irregular cells 

 which have no definite orientation and are very loosely arranged. 

 Notice that in many instances adjacent cells of the spongy par- 

 enchyma touch each other at their narrowest points so that the 

 maximum of wall surface borders upon the large air spaces. 

 The cells contain a peripheral protoplast and a smaller number 

 of chloroplasts than occurs in the cells of the palisade parenchyma. 

 The spongy parenchyma has at least two important functions. 

 First, because of its loosely arranged cells, it acts as a "ventilat- 

 ing tissue" of the leaf, i.e., diffusion of COi.. w^ater vapor and O2 

 between the air lacunae and the cells can take place with relative 

 ease. Second, the spongy parenchyma carries on some photo- 

 synthesis although this function is more efficiently performed by 

 the palisade parenchyma. According to Haberlandt (p. 287) no 

 trans-location takes place from one palisade-cell to another but 

 "the stream of synthetic products" follows the long ajrcs of these 

 elements. Some anatomical evidence in support of this view is 

 furnished by the fact that small groups of 2-10 palisade cells in 



