194 KANSAS UNIVERSITY SCIENCE BULLETIN. 



From the above figures it is seen that the paHsade cells occur 

 most frequently bordering on the water-storage cells, there be- 

 ing nearly three times as many bordering on the water-storage 

 cells as on the veins and twice as many bordering on the veins 

 as on the spongy parenchyma cells. Figure 27 is a diagram- 

 matic drawing, showing the distribution of water-storage cells, 

 b, as seen in a cross section of a leaf. In figure 28 are shown 

 the palisade cells, B, bordering on water-storage cells, A. In 

 figure 29 are shown the palisade cells, A, bordering on the 

 veins, C. Some places in the leaf the palisade cells, D, have 

 still greater access to water, bordering as they do on both 

 water-storage cells, A, and storage tracheids, C. This relation 

 generally occurs at the ends of the leaf. In figure 30 are 

 shown the palisade cells as found in this relation. ^ Sometimes 

 the palisade cells are found bordering on water-storage cells, 

 A, which in turn border on veins, C, as shown in figure 31. 

 Such an arrangement as this is an excellent one; for as fast 

 as the water-storage cells are deprived of the supply of water 

 on hand they can immediately draw on the veins and thereby 

 continue to supply the palisade cells with water as it is needed. 

 In figure 32 are shown palisade cells. A, bordering on spongy 

 parenchyma cells, B. 



Another means for storage of water is the water-storage 

 tracheids found at the termination of the veins. Palisade 

 cells bordering on these tracheids can obtain water when there 

 is need. In figure 33 are shown these tracheids as they ap- 

 pear at the ultimate ends of the veins ; in figure 34 the water- 

 storage tracheids as they appear in other places in the leaf. 



The Aerating Spaces. — In Townsendia there were found 

 devoted to aeration only 20 sq, mm. of the surface of a leaf 

 which measured 100 sq. mm, ; or, in other words, the volume 

 of the intercellular spaces and the volume of the whole leaf, 

 roughly estimated, stand in the relation to each other as 

 8:1000. When compared with Pistia texensis, an hydrophyte, 

 whose aerating volume and the volume of the whole leaf 

 stand in the relation to each other as 760 : 1000, the amount 

 of volume devoted to aeration in Townsendia seems quite 

 small. 



There were found on either side of the leaf an approximate 

 average of 344 stomata to 1 sq. mm., the average number 

 usually found in plants. There was no difference in the char- 



