MINUTE STRUCTURE OF PLANT HYBRIDS. 251 



grains of the first (fig. 16) are like those of H. Gardnerianum, except that they are larger 

 (18 to 24 /x), and that the lamination is coarse. The grains of the hybrid are larger than 

 those of H. Sadlerianum, and exhibit even more evident lamellae (fig. 17). They measure 

 on the average 40 m, but vary from 30 to 50 n. 



But not unfrequently all of the above hybrids have mixed up with the more 

 typically intermediate ones some which can scarcely, if at all, be distinguished from 

 the small grains peculiar to one parent, while very rarely I have observed grains 

 that were so large and rounded as to pass for those of H. coronarium. Now, when 

 describing the epidermal leucoplasts of Dianthus Grievei (p. 22), it was stated that 

 though the average was nearly 3 /*, some measured 2*5 /* or slightly less, others as much 

 as 3*5 /«. The occurrence of these, and similar minute differences in protoplasmic masses, 

 or in formed materials like starch grains which are due to manufacture by these masses, 

 induced me to prepare a set of micro-photographs, and to project lantern transparencies 

 of these on a 7-ft. screen. Thus it was possible to study their dimensions more exactly 

 than under the microscope. It was then found that while the shape, appearance, and 

 size of most starch grains of Hedychium, of Dianthus leucoplasts, of Geum and Mas- 

 devallia chromoplasts, were intermediate, examples might be got which reverted power- 

 fully to one parent, and, so far as they have yet been studied, the reversion was most 

 frequently towards the parent with the more minute cell-contents. 



Hairs of Rhododendron Species. 



In the hybrids that have been fully described one or two cases presented themselves 

 of parent plants being provided with hairs different from each other in structure, and one 

 only or both of these being inherited by the hybrid. This did not involve a pronounced, 

 if at all discernible, leaning of the hybrid to either parent in naked-eye appearance. 

 Many striking illustrations of this nature are afforded by species of Rhododendron, which 

 further furnish remarkable verifications in the epidermal papillae of the exactness with 

 which microscopic details are handed down from parent to offspring on reduced or enlarged 

 scale, according to the interacting effect of the other parent. 



Many of the Himalayan Bhododendxons, including such well-known species as R. 

 ciliatum, glaucum, formosum, Dalhousiw, Veitchiana, &c, have on their under leaf 

 epidermis brown, brown -red, reddish-green, or green scale hairs, with intramural glands, 

 the structure and development of which have been traced by De Bary.* But most of them 

 further show a fine leaden- white tint, due to the outgrowth of epidermal papillae from many 

 or all of the cells. Others again, such as R. Edgeworthii, have in addition long twisted 

 unicellular hairs, which soon after their first formation get filled with air, and their walls 

 assume a brown colour. I will not now deal with the scale hairs further than to say 

 that in size, colour, and outline they may vary greatly in two parents, and that those of 

 one parent only may be inherited by the hybrid offspring. 



* Comp. Anat. Phan. and Ferns, Eng. ed., 1884, pp. 96-97. 

 VOL. XXXVII. PART I. (NO. 14). 2 O 



