LEAF OF KUTA. 191 



structure, we proceed to cut cross-sections ; these we prepare, 

 perpendicularly to the long axis of the leaflet, in the manner 

 already used by us, viz., by placing the leaflet, for the purpose 

 of cutting, between two pieces of elder-pith, or by packing a 

 number of leaflets together for mutual support. The cross- 

 section shows us, occupying the space between the upper and 

 under surface of the leaf, the mesophyll, or general internal 

 tissue of the leaf. Proceeding from the upper towards the under 

 side we see first the epidermis of the upper side (Fig. 76, ep'), 

 then a double or triple layer of parallel chlorophyll-containing 

 cells, elongated perpendicularly to the surface of the leaf, which 

 we- call the palisade cells or palisade layers. We have already 

 proved by the surface-section that these cells are, laterally, more 

 or less separated from one another ; on the other hand, the two 

 successive layers are closely attached together by their ends. The 

 elements of the second palisade layer (pi") are somewhat less 

 numerous than those of the first ; and two of the outer palisade 

 cells often join on to one of the inner." To these two palisade 

 layers follows a loose tissue, that extends to the epidermis of the 

 under side, and forms a network with wide meshes ; this tissue 

 we call spongy parenchyma ; it contains fewer chlorophyll 

 grains than the palisade tissue. The cells of the upper layer of 

 spongy parenchyma (sp) are closely attached to the inner palisade 

 cells, each one usually joining on to several of the latter cells. 

 None of the palisade cells have their lower or inner ends 

 free ; where this appears to be the case (as in some of the pali- 

 sade cells in the figure), it is simply that the junction does not 

 lie in the plane of the section. So also in the network of the 

 spongy parenchyma, the cells have no free ends; all the cells 

 are connected together by their ends. The lowermost layer of 

 spongy parenchyma (sp'"} is elongated in the direction of the 

 lower epidermis, and more or less perpendicularly to it ; here, 

 therefore, we have a kind of intermediate formation between 

 spongy parenchyma and true palisade parenchyma. The struc- 

 ture of the leaf in respect of both epidermis and internal tissue 

 is, therefore, manifestly different upon upper and under side, and 

 differentiated in such fashion that we may look upon it as 

 dorsiventral, the upper side being considered the dorsal, the 

 under the ventral side. Under the stomata (st) can be seen the 

 air or respiratory chambers (a). Single cells in the spongy 

 parenchyma contain cluster crystals of oxalate of lime (&). 



