216 DR J. M. MACFARLANE ON THE 



i. Lapagena different from the epidermis over the lamina. These small cells abut directly against the 



rosea. r jo 



;. Phiiageria indurated elements round the bundle, so that the palisade parenchyma of the leaf is sharply 

 ?. piniesia buxi- interrupted in its continuity along this line. In % the female parent is more nearly 

 approached, but a slight flattening of its epidermal cells occurs, and the cells con- 

 tinuous with the palisade layer become shallower above the indurated sheath. 



In 1 the parenchyma beneath the sheath and next to the lower epidermis is largely 

 developed, there being four to five layers of rounded, loose-looking, and often thick- walled 

 cells. In 3 a single layer only occurs beneath the bundle, and its cells are thin walled, 

 while in 2 there are two to three layers, and some of the cells in these are slightly 

 indurated after the type of 1. 



The upper mesophyll of 1 is made up of three to four palisade cell layers, which, 

 however, scarcely deserve the name in its ordinary application, as the cell elements 

 are quadrangular or isodiametric. They measure on the average 35 //. in depth and 

 width. The intercellular spaces between these are of considerable size. The spongy 

 mesophyll is one and a quarter to one and a half times as deep as the upper, and is 

 composed of rounded or branching cells separated by cavernous intercellular spaces. In 

 old leaves the walls may be strengthened by reticulate or hoop-like secondary deposits. 

 The mesophyll of 3 is made up of two palisade cell layers, which pass by abrupt transition 

 into a dense spongy lower zone. The cells in the uppermost of the two palisade layers 

 are closely packed, and are three and a half times deeper than broad, those of the lower 

 are two to two and a half times deeper than broad, the former measuring 110 by 30 [x, the 

 latter 75 by 35 /a. The cells of the spongy zone are very irregular in shape, usually 

 closely pressed against each other, but may have small cavernous spaces. In 2 the two 

 uppermost layers are clearly defined as a palisade tissue, and traces of a third may 

 be distinguished. The cells of the top layer are 70 to 80 /a deep by 35 [x wide, and those 

 of the subjacent one 50 to 60 fx deep by 35 /x wide. Though fewer and smaller than in 

 the parent, intercellular spaces like those in 1 occur between the walls of the palisade cells. 



The median vascular bundle with its indurated sheath is in the proportion of 10 in 1 

 to 9 in the hybrid and 8 to 8^ in 3, but the relative size and amount of tissue components 

 differ strikingly. In 1 the masses of sheath tissue and of bundle tissue are nearly equal in 

 amount ; in % the sheath tissue is considerably in excess of the bundle tissue, the propor- 

 tion being as 1\ or 3 : 1 ; while in 3 the sheath is strongly developed, and is in proportion 

 to the bundle as 5 : 1. The indurated cells in 1 are thick walled, isodiametric, and uniform 

 with each other, measuring on the average 20 [x across. The vascular bundle tissue is oval 

 or circular in outline, and its main mass is made up of wood vasa and tracheids, the largest 

 of the former being 20 /x across. The indurated cells of 3 are mostly large round the periphery, 

 and measure 37 to 40 ll across, the inner are densely-packed, small, thick-walled cells, 

 irregular in shape, and dissimilar with each other, but the average measurement is 

 20 to 25 /x across. The small bundle is lanceolate in outline, with wood scarcely larger 

 than bast, and the largest vasa measure 10 to 12 fx across. In 2 the indurated cells are 

 larger externally, where they measure 30 to 32 [x ; internally they are denser and average 



