42 TOPOGRAPHY OF CHLOROPHYLL APPARATUS IN DESERT PLANTS. 
chlorophyll tissue during the most of the year in Parkinsonia and Zizyphus 
parryt. 
12. The volume of the chlorophyll band for a unit stem has a value of 
1 in Celtis, 4.1 in Keberlinia, 4.7 in Parkinsonia, and 5.7 in Prosopis. The 
least volume occurs in evergreen forms; the greatest in plants which depend 
in part or entirely on it for photosynthesis. 
13. The thickest chlorophyll band is in Parkinsonia, which is 246 win a 
stem 4.9 cm. in diameter. The thinnest band is in Ce/#is, which is 25 » in 
in a stem 1 cm. in diameter. 
14. Chlorophyll usually disappears early from the woody portion of the 
stem, but in Parkinsonia it may be found in stems 1 cm. in diameter. 
15. When the chlorophyll band is palisade, the character of the palisade 
is very similar to that of the leaf of the same plant. 
16. The following species were studied: Aster spinosus Benth., Baccharis 
enoryi Gray, Celtis pallida Torr., Cereus giganteus Englm., Condalia spathu- 
laca Gray, Covillea tridentata Vail, Ephedra antisyphilitica C. A. Meyer, 
Fouquieria splendens Englm., Franseria dumosa Gray, Krameria canescens 
Gray, Keberlinia spinosa Zucc., Olneya tesota Gray, Parkinsonia aculeata 
L., Parkinsonia microphylla Torr., Parkinsonia torreyana Watson, Prosopis 
velutina Wooton, Salix nigra Marsh,, Sambucus mexicana Presl., Zizyphus 
parryi Torr. 
