ENDS AND CONNECTIONS OF THE BUNDLES. 



375 



spoon, and have on the upper, somewhat concave surface of the latter the same three 

 superficial layers as the middle teeth, while the edge and under-side consist of an ordinary 

 one-layered epidermis. Under the three-layered portion of the surface lies a group of 

 tracheides, corresponding to it in position, which are of the same structure as those of 

 the middle teeth, and are connected with the network of bundles of the lamina by means 

 usually of 2-3 spiral vessels. 



On the inner surface of the pitcher of Nepenthes branches 1-3 vessels thick, coming 

 obliquely from the netwoi-k of bundles, end directly beneath the basal part of the 

 digestive glands considered at p. loi, but by no means beneath all of tljem. Most of 

 these organs, on the other hand, have no bundle-ends extending to them like those of 

 other plants mentioned above. 



Most bundles, which terminate beneath water-pores or glandular parts of the 

 epidermis ', consist of rows of tracheides, perhaps also of vessels, which run parallel 

 towards the point of termination, diverging directly beneath the latter at greater or 

 less angles, and then ending blind. The structure of the terminal elements is the 

 same as in the internal ends; in species of Crassula reticulated tracheides with 

 unusually large meshes occur. In all cases investigated, except Crassula, rows of 

 delicate, smooth-walled cells, elongated in the same direction as the tracheae, lie 

 among the latter without any definite arrangement. These become more numerous 



Fiff. 177. 



Figs. 177, 178.— Primula sinensis. Fig. 177 (.Jo). Outline of a toothof the leaf with its branches of the bundles. The thick- 

 est of the latter ends below the water-pore/ — Fig. 178 (145). -Longitudinal section vertical to the surface of theleaf, through 

 the middle of a similar tooth. upper, w lower surface of the leaf; p water-pore, below which is the air-cavity, and then the 

 epithema, the cells of which are drawn somewhat too large. It contains a little chlorophyll throughout, and the bundle of 

 tracheides,^, ends in contact with it Under the epidermis on both sides is parenchyma containing abundant chlorophyll. 



as the tracheae between them terminate or diverge, and pass over gradually into 

 a group of small delicate cells, which covers the ends of the vessels ; these are in 

 their turn immediately covered by the epidermis, and with reference to the former 

 relation may be called the Cover, Epithema '\ of the end of the bundle. Either a single 



' Compare p. 50, § 8, and p. 90. Most of the literature there cited refers also to the subject 

 treated of here. [See also Gardiner, on the development of the water glands in Saxifraga crustata, 

 Quart. Jour. Micr. Sci. July, 1881.] 



'' im0rjija, the cover. 



