230 



DR J. M. MACFARLANE ON THE 



/. Ribes Grossu- 



laria. 

 8, Ribes Culver- 



wellii. 

 .;. Ribes nigrum. 



amount and constituents of the protoxylem are of interest, I may pass to the tracheids 

 and pitted vasa after drawing attention to the figures. The secondary xylem of the first 

 year is mainly built up of tracheids that are strongly indurated and mostly quadrangular 

 in outline ; the vasa are scant, and 18 to 20 /* across. That of 3 has tracheids that are 

 moderately thickened, and show a large cell cavity, each is 2\ to 3 times as broad as 

 deep ; the vasa are very numerous, giving an open porous appearance to the wood, and 

 they are 25 to 28 [i across. The elements of # are very evenly intermediate. 



The amount of pith relatively is as 3 in 1 to 5 in 2 and 6 to 6^ in 3. The pith-cells 

 in 1 are circular in outline, the majority of them store starch, and they develop consider- 

 able secondary thickening. The pith of 3 appears loose, not only from the large size of the 

 intercellular spaces, but because many large cells are devoid of starch contents. All of 

 them are polygonal in outline, and the amount of secondary thickening is small. 

 While the condition is an intermediate one in %, there is a decided leaning toward the 

 latter. The starch grains of the three are very variable in size, but in 1 the largest are 7 fi 

 and the average 4 m. In 3 the largest are 3 and the average 1^ m. In 2 the largest are 

 5 and the average 3 /a. 



Leaf-Stalk. — In 1 the margins of each leaf-base show short, club-shaped gland hairs, 

 which higher up become elongated, and some of these may have secondary hair processes 

 branching out from them. In 3 there may be three to eight of the branched hairs, but 

 devoid of the club-shaped glandular top ; also an abundance of slender, simple hairs. But 

 specially noteworthy are sessile, multicellular, button-shaped gland hairs of a greenish 

 colour, which are also abundant over the lamina, and secrete the characteristic scent of the 

 black currant. In 2 the short basal hairs and elongated club-shaped upper hairs are both 

 present ; the latter at times resembling the currant parent, in being without terminal knob 

 though provided with lateral branch hairs. Dispersed over the surface also are greenish 

 gland hairs, reproduced from the currant parent, though about half the size. The size and 

 shape of the leaf -stalk epidermal cells in 2 are exactly intermediate between those of the 

 parents, and the same applies to the base and upper part of the petiole when these are 

 examined in section. 



Leaf. — The lower leaf- epidermis of 1 (Plate V. fig. 11) shows irregular cells, with wavy 

 walls, that are tolerably thickened, and from some of these arise strong thick-walled, simple 

 hairs. Over a given area an average of twenty-seven stomata was recorded. In 3 (fig. 13) 

 the cells are straight or flexuous in their walls, which are very thin, and the size of each cell 

 averages half the size of one in the former. While delicate hairs are plentiful along the 

 veins, they are absent over the areas between, which, however, show many large greenish 

 gland hairs. An average of forty-two stomata occurs over a like area as in the last. 

 Here, as in the leaf-stalk, the hybrid reproduces the diffuse hairs of the first parent and 

 gland hairs of the last, though reduced by half according to careful measurement. 



In the leaf-bundle of 1 the external bundle elements are filled with a dense brown- 

 yellow substance, which is absent in the other parent, but comes up in the hybrid as a 

 pale yellowish pigment. 



