278 



PHOTOSYNTHETIC SYSTEM 



Acanihopanax, Cussonia, Schwenkia, Chloranthus, Phyllanthus, etc. In- 

 stances of their occurrence in Monocotyledons are afforded by certain 

 species of Bambusa and Arundinaria, further by the genera Elymus 

 and Calamagrostis, and by Alstroemeria psittacina. Gyranosperms are 

 represented in this connection by the genera Pinus and Cedras, and 

 Ferns by Aspidium aculeatum, A. Sieboldi, Lomaria gibba, Todca aspera, 

 Didymochlaena sinuosa, and various species of Adiantum (Fig. 110 c). 



Fig. 110. 



Arm -palisade- tissue hi various leaves. A. Pinus Laricio (T.S.). In the cells imme- 

 diately below the hypodermis the flanges (J\) are all arranged at right angles to the 

 leaf-surface ; in the more deeply-seated layers they are disposed in various planes. 

 B. Sambucus nigra (T.S.). C. Adiantum trapeziforme ; the arm-palisade layer is 

 protodermal in origin. Cell-contents omitted in all the figures. Arm-palisade-cells 

 shaded in B and C. 



The characteristic flanges may develop only from the upper or epidermal 

 end of the cell, in which case the cell-cavity is continuous as regards 

 the lower half of the cell, while above it is divided into two or more 

 branches or arms ; in other instances (e.g. Anemone sylvestris and 

 Clematis recta) folds arise from both ends of the cell, thus giving rise 

 to the H-shaped elements noted above in the case of Pinus. In Bam- 

 busa Simonii, again, the flanges are only developed in connection with 

 the lower ends of the tabular green cells ; the photosynthetic elements 

 of Ferns also often conform to this comb-like or pectinate type, though 

 in their case additional flanges are not infrequently present on the 

 radial walls. The number of " arms " developed by each cell is most 

 often three or four, but ranges from two in Galtha palustris to eight or 

 more in Todca aspera. The length of the flanges usually amounts to 

 between one-third and two-thirds of the radial diameter of the cell. 



The foregoing interpretation of the arm-palisade-cell as a modifica- 

 tion of the typical palisade-cell introduces the conception of a palisade- 



