70 THE WATERLILIES. 



assume the most grotesque shapes ; one might truly say that of the 

 thousands one sees, no two are alike. Since most of the arms end freely 

 in open cavities, as do those in the air-canals of the roots, petioles, and 

 peduncles, it is impossible to assign to them any function of strengthening 

 the tissues as Arcangeli (1890, a) suggested, although bipolar and H- 

 shaped idioblasts in leaves may have that use in a measure. Arcangeli's 

 additional opinion that they serve as depositories for waste calcium 

 oxalate seems to be a good one, although Kohl (1889) reverses the case 

 and considers that in all such cases the salt is a by-product of the 

 deposition of thickening carbohydrates on the cell-wall ; he imagines that 

 the glucose or dextrose is transported as a calcium compound. There 

 are, however, great numbers of idioblasts in the leaf, of still another type, 

 which seem to have a definite supporting office. These are cells of great 

 size, with one end spread out in three or four lobes against the inner side 

 of the upper epidermis ; from this broad base a stout shaft runs down 

 between the strings of palisade cells (Fig. 30, id}. Reaching the spongy 

 parenchyma, it may break up at once into several radiating arms, or may 

 continue straight on down to the lower epidermis and attach itself there 

 by a narrow base ; all imaginable intermediate conditions may be found. 

 The walls of such idioblasts are extremely heavily thickened. In dried 

 specimens these make prominences on the upper surface of the leaves, 

 and since their number differs according to the species, they were used 

 by Caspary (pachycysts, 1865) for systematic distinctions. 



The veins which ramify copiously throughout the leaf present several 

 interesting features. The midrib is marked by a line of modified paren- 

 chyma. In the palisade region this line is three to five cells wide. The cells 

 are nearly cubical and very poor in chlorophyll ; the upper ones have 

 thickened walls. These grade off insensibly into a plate of larger, close- 

 fitting parenchyma cells which runs through the leaf to the lower epidermis. 

 There is a broad arc of corner-collenchyma just within the epidermis on 

 the lower side of the rib. Embedded in the plate of parenchyma are the 

 vascular bundles, and along its sides are two (N. odorata} to several 

 (N. rubra, zanzibaricnsisy.} air-canals. Each vascular bundle is sur- 

 rounded by a sheath of parenchyma cells much smaller than those of the 

 neighboring tissue. Although a well-developed xylem of spiral tracheae 

 and companion cells is present, it is less in amount than the phloem. 

 Near the base of the midrib several types and positions of bundle are met 

 with (Fig. 31 ). In A r . odorata there is shortly below the epidermis a tiny 

 bundle, and just below this a much larger one, both with xylem above and 



