222 



DR J. M. MACFARLANE ON THE 



/. Dianthus 

 alpinus. 



t, Dianthus 

 Grievei. 



... Dianthus 

 barbatus. 



When the middle part of the aerial flowering stem is examined, i.e. the part towards 

 the base of the third internode in 1, of the fifth in #, and of the seventh in 3, the cuticle 

 of the epidermis is in proportion of 1^ to 2 J to 3. The outer cortex in 1 is made up of nine 

 to ten chlorophyll layers ; in 2 of seven to eight ; in 3 of six. The innermost layer is 

 largest in all, but the cells in the three are in the proportion of 5:4: 3. The inner cortex 

 is a strengthening sclerenchyma, which in 1 consists of four to five specially thickened 

 external bands merging gradually into an inner series of five to six, which become less 

 and less thickened. In 3 the two outer layers are greatly thickened, dense, and of small 

 size, and abruptly pass into an inner zone, which has thin-walled elements grouped into 

 eleven or twelve layers. A condition nearly between these exists in the hybrid. 



When the inner cells are minutely examined under a power of 600", those of 1 show 

 extremely little thickening, with at times one pore-canal along a wall side ; in 3 the thicken- 

 ing is very pronounced, and three or more pore-canals can be observed along the side ; while 

 l 2 has an intermediate amount of thickening and number of pore-canals. The phloem 

 does not call for special attention. 



The xylem of 1 consists of a cylinder of spiral tracheae, the number of which in a 

 section such as we now describe amounts to 370 ; in % to 720 ; and in 3 to 1260. The 

 diameters of the tracheae are in proportion as 3 : 4 or 4 '5 : 6. In longitudinal view the 

 stem epidermis of the three shows a considerable abundance of stomata in line with the 

 halves of the leaf lamina, but an absence in line with the leaf midrib, and the areas between 

 the leaves. On the average, in 1 there are nine under Zeiss' high power with 4 eyepiece ; in 

 2 there are seven ; and in 3 there are five. The epidermal cells of the first are 120 ft long, 

 slightly wavy in outline, and contain leucoplasts 2 /x, in diameter, which, with the nucleus, 

 stain a deep pink hue in eosin solution. Those of 3 are 50 (i long, have straight, 

 thickened walls, and the leucoplasts are 4 /a across. In % the cells are about 90 /x long, 

 straight or slightly sinuous — not wavy — in outline, and the leucoplasts are in most cases 

 about 3 /*. across. It may further be noted that, as the result probably of mechanical 

 rather than vital conditions, the cell nucleus in 1 is lenticular, due, I should suppose, to 

 elongation by movement in the streaming protoplasm of the long cells. In 3 the nucleus 

 is spherical or slightly oval, while that of the hybrid decidedly leans to the first. 



The green subepidermal cortex cells in all have conglomerate crystals. But it may 

 here be stated that I have found crystals to be the most unsatisfactory and unreliable of 

 any cell content. In these, however, a rather striking and very constant condition can 

 be traced. In 1 they are few but large, each being 50 jjl across ; in 3 they are very abund- 

 ant but only 30 /a across ; in the hybrid they are more abundant than in 1, less . so than 

 in 3, while their size is 35 to 38 jjl. 



The outer cortex is an interesting study, but I shall only compare the two external 

 layers of it. In 1 the cells are twice to three times as long as deep, are columnar in 

 shape, and have on the average a length of 80 //., while a few small intercellular spaces 

 occur between the common walls. The chloroplasts are 3 //, across, and, though rather 

 more abundant in the two layers now described, are pretty uniformly distributed through- 



