MINUTE STRUCTURE OF PLANT HYBRIDS. 



239 



short thick stalk and greatly enlarged oval head, are about as frequent as are the long-stalked 

 ones on the other parent. Bryanthus is quite intermediate in cell size, shape, wall thicken- 

 ing, and pore distribution. Four stomata is the average in an area corresponding to that 

 cited above. The curved hairs are reproduced in the hybrid, and glandular hairs, reduced 

 in size but similar to those on both parents, are found on adjoining parts of the same tissue. 



On transverse section the cortex in the three shows an outer and inner cellular layer, 

 with sclerenchyma ring separating them. In 1 the sclerenchyma elements are thick- 

 walled and small,, the largest being 12 //, across ; in 3 the elements are slightly thickened, 

 but measure 18 to 20 /x ; in 2 the moderately thickened elements are 15 to 16 [x across. 

 The tissues of phloem and xylem closely agree in all, except that the pitted vasa of 3 are 

 in cross section and relative number half those of 1, while the hybrid is a mean between 

 them. 



The amount of pith tissue is as 5 : 4 : 3. The pith is made up of large clear cells, and 

 of others which are starch storers, with slightly-thickened pore-marked walls. The latter 

 predominate in 3, and they form a reticulate mass which surrounds the longer rounded 

 cells. In 1 the former type predominates, the clear cells enclosing patches of starch- 

 storing cells. In 2 both types are very uniformly distributed, though at times there is 

 a morphological bias towards 3. 



Longitudinal sections of the stem add little to the above, except as to pith tissue. 

 The starch-storing cells of 3 are equilateral, or, more commonly, slightly broader than 

 long ; each is on the average 20 /x, and a large amount of starch is stored. The starch 

 grains are 4 ju across at their largest, though most are from 2 to 3 /x. The clear cells 

 are 70 to 80 /jl long, and never store crystals. In 1 the starch-storing cells may be 

 quadrangular, but on the average they are 1^ times broader than long, and a small 

 amount relatively of starch is stored. The largest starch granules are 6 m across, and in 

 all cases they are larger than in 3. The clear cells are 150 to 200 m long, and occasion- 

 ally contains conglomerate crystals, 16m across. In 2 the starch-storing cells may incline 

 towards one parent or the other in size, though the amount of starch stored and the size 

 of the granules fall rather towards 3. The same is true of the clear cells, but a marked 

 peculiarity, observed, however, by me in two other hybrids, is that the power of con- 

 glomerate crystal formation is not only inherited from the male parent, but appears on 

 a more exaggerated scale, there being at least 50 per cent, more crystals in a given area 

 of the hybrid pith than in that of the parent. This may point to a greater formation of 

 waste products in the hybrid, but better and wider evidence must be forthcoming before 

 a final conclusion can be reached. 



Leaf. — In the three the upper epidermal cells are wavy in outline ; in 3 they are twice 

 the size of those in 1, and intermediate in the hybrid. On the lower epidermis the cells, 

 though smaller throughout, are in the ratio of 9 : 7 : 5. In 3, thirty to thirty-three stomata 

 are visible under Zeiss' D with 4 eyepiece. In 1 there are seventy to seventy-five, and in 2, 

 fifty to fifty-five. In 3, hairs are entirely absent from the under epidermis. In 1, recurved 

 hairs like those of the stem grow out abundantly from the lower epidermis, interspersed 



1. Menziesia 



empetriformis, 

 var. 



2. Bryanthus 



erectus. 



3. Rhododendron 



Chamsecistus. 



