. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. t plantsof course vary from this in certaindetails. In the leaf of the India rubbertree, Ficus elastica (Fig. 79), at theupper surface the epidermis is suc-ceeded by a clear tissue two to threecell-layers deep which serves as awater-storage tissue. Then followtwo to four layers of palisade cells,several layers of spongy cells, twoto three layers of relatively small water-storage cells, and last the lower epidermis. In the spacesbetween the veins where the palisade cells cannot co


. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. t plantsof course vary from this in certaindetails. In the leaf of the India rubbertree, Ficus elastica (Fig. 79), at theupper surface the epidermis is suc-ceeded by a clear tissue two to threecell-layers deep which serves as awater-storage tissue. Then followtwo to four layers of palisade cells,several layers of spongy cells, twoto three layers of relatively small water-storage cells, and last the lower epidermis. In the spacesbetween the veins where the palisade cells cannot communicatedirectly with the food-conducting cells the spongy cells collectthe products of the palisade cells and deliver them to the veinsby the indirect route shown in Fig. 79. This device is by nomeans peculiar to the rubber leaf, but is very generally employed. In Indian corn each of the veinlets is surrounded by a sheathof border parenchyma cells, and these in turn by palisade cellsradiating from them, as shown in Fig. 80. In corn, as indeedin many grasses, starch is not formed in the palisade cells at all,. Spongyparenchyma Water storage tissue FIG. 79.—Cross section througha portion of rubber leaf, showing thelarge percentage of water-storagetissues on both sides of the leaf,and the relation of the palisade andspongy parenchyma to the lateralveins. 148 CONSTRUCTION OF PLANTS FOOD


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