16 



and fibrous masses grow tliicker beneatli the colorless parenoliyina 

 while they decrease under the biuidles. The form of the section becomes 

 more and more closed until near the apex it assumes a palette or a. cir- 

 ular shape (fig. 5, PI. YIII). Here the center consists of a few large cells 

 with scanty chlorophyll contents, but the rest is occupied by thickened 

 cells of various sizes, all, however, with distinct lamination and con- 

 spicuous radial canals. As long as chlorophyll tissue a;)pears near the 

 surface, even in the tliorn-like tip, stomata are to be found in the outer 

 epidermis. 



The S plant of J. sframinea does not differ much from that of J.pilom^ 

 except that it is smaller and less rigid. Anatomical differences are 

 not more pronounced. The fibrous tissue is very slightly developed; 

 the cells are few and their walls thin, even in the strand at the margin 

 of the leaf, and the strands under and above the bundles are reduced 

 to one or two cells. The 9 plant, on the other hand, is widely differ- 

 ent from the $ plant of the same species. When drj^, the leaves are 

 flat except at the apex, which is somewhat involutely folded. They are 

 less rigid than those of the staminate plant, and the apex is not pun- 

 gently pointed. One or two young leaves, however, at the apex of each 

 shoot are conduplicate, and are curved backward as in the male plant. 

 The transverse section of one of these reveals the presence of ridges and 

 furrows, and the bulliform cells are much smaller than those of older 

 leaves of the same shoot. This difference is wholly due to the unde- 

 veloped condition of the bulliform cells consequent on the immaturity 

 of the leaf. The flat leaves have usually one or two nerves of one 

 margin folded inward for the whole length of the leaf, and it is this 

 bend that, by bringing the margins close together, is chiefly responsible 

 for the involute or conduplicate folding of the leaf at its apex. 



A transverse section (fig. 6, PI. IX) shows that the veins do not form 

 ridges, but are, on the contrary, often depressed below the level of the 

 bands of prominent bulliform cells. The veins of the basal portion of 

 the leaf are covered for a short distance with numerous prickles. With 

 the exception of these and of a few others sparsely scattered along the 

 nerves and margins, the upper epidermis has no exodermal expjinsions 

 proi^er, though the club-shaiied cells that cover the chlorophyll jiaren- 

 chyma overlap in such a way as to make the larger end of the cell some- 

 what prominent. It is chiefly remarkable for the size and number of 

 bulliform cells (tig. <i, B, PI. IX), which are arranged in from 5 to 7 rows, 

 the central one being very acute at the summit and very broad at the 

 base, the 1 iteral cells (fig. 0, />, PI. IX) narrow and deep and projecting 

 far beyond the stomata which border them, so that in surface view the 

 latter are almost hidden. A longitudinal section shows that the length 

 of the bulliform cells is never as great as their depth, and also that the 

 underlying colorless cells are two or three tinu'S as long as tlie bulli- 

 form cells. Toward the apex of the leaf there are a few prickles along 

 the nerve that marks'the marginal fold; otherwise the lower epidermis 



