STRUCTURE. 81 



We will now take up some details relating to the individual floral 

 organs. The line of insertion of the sepals is usually smooth and 

 rounded ; but in N. Candida the bases of the sepals are slightly produced 

 downward, and in N. fennica the sepals make a sharp, clean-cut angle 

 with the receptacle. The general shape of the sepals is ovate. They 

 are always greenish and chlorophylloid outside, and soft and petaloid 

 inside ; the margins which are covered in the bud are wholly petaloid. 

 Specific details of shape, size, color, and texture are given in the taxo- 

 nomic portion of this paper. The epidermis of the outside of the sepals has 

 a very smooth surface, and consists of irregularly polygonal cells in sur- 

 face view, nearly square in section. Bases of mucilage hairs are frequent 

 in N. tuberosa and plentiful in N. odorata. In the latter species, also, 

 stomata are present. They begin at or just below the middle of the sepal 

 and are more plentiful toward the apex and are a little larger than those 

 of the leaf (0.015 by 0.015 mm.). The cells of the inner epidermis are 

 rounded and prominent on the exposed side, of approximately rectangular 

 shape, and shallower than those of the back of the sepal. Here also 

 rounded cells like the bases of mucilage hairs are frequent, but no stomata. 

 The parenchyma of the sepal is traversed longitudinally by vascular 

 bundles and in the lower parts by air-canals. Inside the outer epidermis 

 there are in N. zanzibariensis x about 8 tiers of close-fitting, nearly spherical 

 cells containing chlorophyll ; they become gradually larger from without 

 inward. Then follow i or 2 flattened cells and a vascular bundle, or, 

 between the bundles, 2 to 4 flattened cells and an air-canal. About 5 

 roundish cells intervene between the air-canals and the inner epidermis. 

 At the apex of the sepals the structure differs from this only in the 

 absence of air-canals. Just within the epidermis on each side two or three 

 layers of cells are feebly collenchymatous, but most noticeably so on the inner 

 side of the sepal. The air-canals in this hybrid are rather large, round or 

 oval, and arranged in a single row between the middle of the parenchyma 

 and the inner epidermis. The partitions between them are two or 

 three to several cells thick. The vascular bundles have a well-developed 

 protoxylem, and at some distance from this, in the larger ones, a small 

 air-canal. There is a row of larger bundles about the middle of the 

 parenchyma and a row of smaller ones between the air-canals and the 

 inner epidermis, with still others between the canals. Many stellate 

 idioblasts project into the air-canals, but none was found elsewhere in 

 these sepals. Thyll-like ingrowths also occur. One of these consisted of 

 but two dense clavate cells, another had a multicellular base surmounted 

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