8 



TOPOGRAPHY OF CHLOROPHYLL APPARATUS IN DESERT PLANTS. 



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' ' v . '.'' ': "'.V* *'.-.:'. ' \. 



chlorencliyma of the leaf was observed also in I\raiucria cancscens, where 

 the cortical chlorophyll band is likewise palisade. 



CELTIS PALLIDA. (Plate 2, B, and figs. 2 and 3.) 



The specimen of Ccltis which was chosen for study is growing in the 

 arroyo below and to the east of the Laboratory building". A branch about 

 2 in. in length was selected and sections made at the following distances 

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

 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 

 general structural 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 y 1 1 band 



FIG. 2. Celtis pallida: A, section of branch 2 mm. in diam- \yhich is also about 

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



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 largely 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 medullary 

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



\ \ S..J....L.2 .._=:.. J i ' 'fo-. 



/, _, _-""* * " -*..: * 



""" " 



B 



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

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

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

 enduring chlorophyll tissue in the stem. 



