bunton: lesquerella spathulata. 205 



water-conducting tissues. The tracheal tissues consist of 

 spiral and scalariform tracheal tubes and tracheids. 



5. Photosynthetic Tissues. — The photosynthetic tissues of 

 the leaf consist exclusively of palisade cells, and there is found 

 in a single palisade cell on either side of the leaf an average of 

 twenty-seven chloroplasts. 



6. Food-conducting Tissues. — As in Townsendia, the 

 phloem is but little differentiated. It consists exclusively of 

 undivided mother cells of the sieve tubes; sieve tubes and 

 sieve parenchyma cells are wholly lacking. 



7. Storage Tissues. — In the stem the phloem cells and 

 medullary-ray cells afford provision for the storage of food. 

 In these tissues starch and proteids were stored up in small 

 quantities. The only storage tissues found in the leaf are the 

 large stellate hairs which, possibly, rapidly fill whenever the 

 water supply is increased, and, being cellulose-walled at their 

 bases, yield their contents to the mesophyll cells as the supply 

 of water is reduced. 



8. Aerating Spaces. — As would be expected to be found in 

 a xerophyte, the amount of space devoted to aeration is com- 

 paratively small, there being only 2.7 per cent of the volume of 

 the leaf devoted to this purpose. 



4-Univ. Sci. Bull , Vol. V, No. 11. 



