MINUTE STRUCTURE OF PLANT HYBRIDS. 271 



relation to colour formation noticed in the sepal of Cypripedium Leeanum may also be 

 noted here. 



In the formation of nectaries as traced in Philageria, Dianthus, Saxifraga, Ribes, 

 &c, the above principles also hold. 



The distribution of stomata over any epidermal area has been proved to be a mean 

 between the extremes of the parents, if the stomata of the parents occur over one surface 

 or both, and if the leaves are similar in consistence, but, as in Iledychium Sadlerianum, 

 and to a less degree in Saxifraga Andrewsii, if the stomatic distribution and leaf con- 

 sistence differ in the parents, this may give rise to correspondingly different results in 

 the hybrid. 



In amount of cuticular deposit, and arrangement of it into ridges or other localized 

 growths, hybrids have been proved intermediate between the parents. We may merely 

 recall here the case of Philageria stem, which inherited cuticular ridges from Lapageria, 

 though reduced to half the size, since the Philesia parent was devoid of them. 



As Wichura has already proved for the vegetative leaves of hybrid willows, the 

 venation of hybrid leaves is very uniformly intermediate between those of the 

 parents. Figures are given with this paper of the vegetative leaves of Philageria and 

 Saxifraga, and of the petals of Dianthus and Geum. The relation of the bundles to 

 special terminations, as in the water stomata of Saxifraga. is in conformity with the 

 venation. 



But the growth of tissue in a hybrid which is to determine the outline or angular 

 position which any organ or part of one will assume is intermediate between those of the 

 parents when the latter show traceable differences. Thus the sepals and petals, as also 

 the styles and style-arms, of Geum intermedium, the floral parts as a whole of Saxifraga 

 Andrewsii and Ribes Culverwellii, the frilling of some of the floral parts of Bryanthus 

 and Cypripedium Leeanum are pronounced cases, while minor ones have been referred to. 



Turning to minuter anatomical details, every hybrid has yielded a large series of 

 examples which prove that the size, outline, amount of thickening, and localization of 

 growth of cell walls, is, as a rule, intermediate between those of the parents. We have 

 repeatedly stated that as the outcome of growth localization, intercellular spaces of a 

 hybrid are modified in size and shape as are the cells which surround them. Now this 

 clearly demonstrates that the living protoplasm which has formed the cells is so organized 

 in its molecular or micellar constitution that in every cell and over every infinitesimally 

 minute area on its surface where cellulose is to be laid down the balanced effect of both 

 parents is felt. 



Equally in the laying down of secondary wall thickenings, whether of a cuticularized, 

 lignified, or colloid nature, numerous citations have been made where the amount and 

 mode of deposition is evenly between the extremes of the parents. Perhaps the most 

 striking case is that of the bundle-sheath cells of Philageria and its parents, where 

 usually five lignified lamellae are traceable in each cell of Lapageria, eleven or twelve in 

 Philesia, and eight or nine in Philageria. 



