TOPOGRAPHY OF CHLOROPHYLL APPARATUS IN DESERT PLANTS. 



chlorenchyma of the leaf was observed also in Kramcria cancsccns, where 

 the cortical chlorophyll band is likewise palisade. 



Celtis pallida. (Plate 2, u, and figs. 2 and 3.) 



The si:)ccimen of Celtis which was chosen for study is .qrowin.y- in the 



arroyo below and to the east of the Laboratory bnildin.q-. A branch about 



2 m. in lenofth was selected and sections made at the followinq- distances 



from the tip: 6, 21, 34, 49, 64, 79, 144, and 178 cm. The parts of the 



branch where the sec- 

 tions were made had 

 the following- diame- 

 ters: 2, 3.5,4, 4.5, 6, 

 8, 8.5 mm. and 1 and 

 1.6 cm., respectively. 

 A section of a branch 

 2 mm. in diameter and 

 6 cm. from the tip 

 shows the following- 

 ijeneral structiiral re- 

 lations : 



Cortex: There are 

 several well - defined 

 cortical divisions. An 

 epidermis with a thin 

 outer wall and a sub- 

 epidermal tissue about 

 three cells in thick- 

 ness bound the stem. 

 Within this lies a 

 c h 1 o r o p h }• 1 1 band 

 which is also about 

 three cells in thick- 

 ness. A discontinuous ring of hard bast is situated within the chlorophyll 

 band. Between the hard bast and the cambium is the region of the inner 

 cortical parenchyma. 



Woody cylinder: The wood is composed very larg-ely of wood fibers with 

 a noticeably small amount of wood parenchyma. The pith is well marked 

 but does not need further mention in this connection. 



Chlorophyll occurs in the outer cortical parenchyma, in much of the par- 

 enchyma which lies between the hard bast and the wood, in the medullar\- 

 rays, both of wood and of cortex, and in the outer cells of the pith. 



* The term chlorophyll band as used in this paper refers to that portion of the cortical 

 parenchyma tliat lies between the epidermis and the ring of mechanical tissue which is 

 about midway lietween the epidermis and the cambium. It is the largest and the most 

 enduring chlorophyll tissue in the stem. 



Fig. 2.— Celtis pallida: A, section of branch 2 mm. in diam- 

 eter; B, section of branch 3.5 mm. in diameter. 



