l8 9i.J Anatomical Characters of N. Am. Gra?ni?ie<z. 221 



(plate XXI, fig. 4). In U. latifolia there is present a thick- 

 walled parenchymatic tissue between the leptome and had- 

 rome, and the same is also to be observed in U. gracilis and 

 U. nitida, at least in the largest bundles. But neither this 

 stratum nor the inner sheath of thick-walled cells may be 

 considered as indicating any mestome-sheath ; they merely 

 represent a mestome-parenchyma for the same reason as 

 mentioned for U. latifolia. 



The mestome-bundles show, as in U. latifolia, three differ- 

 ent forms depending on their strength and development. 

 Those of the first degree have a closed inner sheath besides a 

 layer of similar thick-walled cells between the leptome and 

 hadrome, while in those of the second degree the leptome and 

 hadrome are in contact with each other. In the smallest bun- 

 dles there is no closed inner sheath of thick-walled cells, 

 but merely an interrupted layer on the leptome side, and the 

 leptome and hadrome are in immediate contact with each 

 other. The leptome and hadrome, considered by themselves, 

 show the strongest development in the largest bundles, those 

 of the first degree. 



As to the distribution of these different forms of mestome- 

 bundles in the entire blade, I do not dare try to give any for- 

 mula, as has been done in U. latifolia. There seem to be too 

 many variations, especially on comparing leaves of specimens 

 from different localities, but it may be said with good reason 

 that the bundles of the second degree are the most numerous 

 in the whole blade, while the largest ones are present in a rel- 

 atively small number. 



On examining the mestome-bundles in U. paniculata and 

 U. Palmeri, there will be seen a rather important difference 

 in structure from what has been shown above. The proper 

 parenchyma-sheath is thin- waited in both species, but con- 

 tains large deposits of starch in U. paniculata (plate XXII, fig. 

 9) and forms a border between the entire mestome-bundle and 

 the mesophyll on both sides. In U. Palmeri (plate XXII, Bg. 

 5) on the contrary it does not contain starch and forms an an- 

 nular .heath around the whole bundle, not extending to the 



epidermis on either of the two faces. 



There is in the largest bundles of U. paniculata a closed 



heath of thick-walled parenchyma around the leptome, while 

 in U. Palmeri both the leptome and hadrome are surrounded 

 b y a similar sheath, besides which the leptome contains sev- 



fal groups, more or less isolated, of very thick-walled cells. 



