32 



of the mestom we see, as we approach the node (Fig. 3, h), the 

 free, pointed ends of some spiral tracheae projecting from the 

 sides and from above into the open space of the canal (Fig. 3, sd). 

 The higher we proceed the more crowded with such free ends of 

 tracheae do we find the interior of the canal, until, at last, we have 

 in place of it, a solid bundle of spiral ducts. We now trace, 

 on longitudinal sections, the course of this bundle through the 

 node, and observe how it divides into anastomosing branches, 

 leading to the leaf of the node, to the axillary buds, eventually to 

 the secondary roots, and to the succeeding intcrnode. Above 

 the node the tracheae terminate as abruptly as they started below 

 it; their free, tapering ends crowd into the end of the canal that 

 belongs to the mestom of the next internode, forming a concave 

 bottom for it just as their opposite ends form a concave roof for 

 the canal in the next lower internode. In the meristematic tissue 

 of the youngest internode we can trace an exceedingly delicate 

 annular vessel, which, however, very soon disappears and is re- 

 placed by the rapidly widening canal of the mestom. The lep- 

 torn elements are continuous through the node. 



The structure of the petiole is like that of the stem, but in place 

 of two mestom bundles there is only one descending to the stem, 

 being, however, in all respects like those of the stem. The con- 

 nection between the homologous parts of petiole and stem is 

 effected in exactly the same manner as just described. 



The thick, oval, peltate leaf, sometimes almost 4 in. long, has, 

 at most, twenty principal veins, converging at the center, over the 

 petiole. The spiral vessels of all these veins empty, as it were, into 

 the central intercellular ,canal of the petiole, or rather, draw the 

 supply of water for the leaf from it, just like a number of distrib- 

 uting pipes that are connected with a large reservoir. The leaf 

 has a smooth, cuticularized upper epidermis with very numerous 

 breathing pores, about 325 on a square millimeter. In the region 

 above the petiole, however, on a oval surface of an average diam- 

 eter of 2.5 mm. there are no stomata at all. 



The cells of the upper epidermis have a peculiar structure. 

 They are two or three times as high as they are wide ; in thin 

 sections their vertical walls at first present the appearance of 



4. 



deeply indented wavy lines, but on closer examination we per- 



