Kl'HKDKA ANTISYPHILITICA. 15 



is, of course, without chlorophyll. However, alibis time, in addition to 

 segments of the original chlorophyll band, there extends beneath the cork at 

 least one layer of cells which are chlorophyllaceous. It does not appear 

 that the i)helloderm contributes to the chlorophyll apparatus. From these 

 circumstances it happens that stems which appear brown or gray in color and 

 give no visible indication of chlorophyll are, however, chlorophyllaceous. 



With the further development of the bark the primary cortex, except the 

 single layer of cells which contain chlorophyll and which lie immediately 

 within the phellogen, is entirely cut off, and with this process the most 

 considerable portion of the chlorenchyma of the stem disappears. When 

 chlorophyll quite left the stem was not learned. In a stem 7.5 mm. in 

 diameter, in which no trace of the primary cortex remained, chlorophyll 

 was to be seen in the outer medullary rays of the woody cylinder, in the 

 rays of the cortex, and sparingly in parenchyma connecting the ends of the 

 latter. Stems 1.1 and 1.5 cm. in diameter give no trace of chlorophyll in 

 either wood or pith. 



FOUQUIERIA SI'LENDENS. ( Fig. 6.) 



Foiiqnicria occurs on dry, well-drained slopes. The plant used in this 

 study is growing on Tumamoc Hill not far below the Laboratory. 



The young stem, 5 mm. in diameter, is characterized by three well- 

 defined areas, namely, (l) an external shell of sclerenchyma, within which 

 is ( 2) parenchyma containing chlorophyll, and within this is (3) the inner 

 cortex, wood, and pith. The relative extent of the three divisions will be 

 apparent from the sketches. The external shell is part of the primary 

 cortex and is morphologically the base of the spines of the stem, which in 

 turn are morphologically midribs of the primary leaves. The cells of the 

 external shell early take on the characteristic thickening and turn brown, 

 and in stems 5 mm. in diameter the shell forms a continuous covering. 

 When the stem increases in diameter, however, the mass of sclerenchyma 

 connected with each spine draws away from the mass connected with every 

 other spine, and the intervening space is occupied by a waxy tissue which 

 is somewhat greenish. The area covered by these two classes of tissue 

 is more and more disproportionate in amount as the stem grows until in 

 the oldest parts the surface is practically all covered by the newer tissue. 



The chlorophyll is confined to the parenchyma, which lies immediately 

 within the shell of sclerenchyma or the newer tissue that succeeds it. Tt 

 is composed wholly of cuboid, thin-walled cells with prominent intercellular 

 spaces. 



So far as I have observed, chlorophyll is always present in the stems of 

 Fouquicria, of whatever size. In stems 5 mm. in diameter the chlorophyll 

 band forms a continuous ring in the outer portion of the cortex. As the 

 shell base of each spine becomes separated from the base of the other con- 

 tiguous spines in the manner above described, breaks occur in the chloro- 



