MINUTE STRUCTURE OF PLANT HYBRIDS. 



247 



tendency towards one or other parent. The relative depths of leaf sections and of the 

 spongy parenchyma in these may merely be referred to as conforming in general effect 

 with what we have given above. 



Flowering Stem. — The surface appearance of most of the epidermal cells agrees in the 

 three. In C. Spicerianum a few four-celled hairs are found just beneath the flower 

 bract, otherwise the stem is glabrous. In C. insigne rounded cells are present over 

 the whole length of the stem, and from these five- or six-celled pointed hairs spring. 

 Glandular hairs are about equally abundant. Each is made up of a stalk of four cells, 

 and a terminal club-shaped part of three cells. In the hybrid both kinds are present, 

 but more sparingly and of smaller size than in the latter parent. 



In C. Spicerianum five to six layers of rounded and neatly arranged cells with 

 thickened walls lie beneath the epidermis. They surround small sharply defined and 

 nearly triangular intercellular spaces. In C. insigne there are ten to twelve la}' - ers of 

 larger and looser cells than in the last, the walls of which are feebly thickened. They 

 surround irregular and rather large intercellular spaces. In the hybrid there are eight 

 to nine layers with moderately thickened walls, and the intercellular spaces are between 

 those of the parents in size and form. The sclerenchyma sheath is alike in the three. 



In the bundle system the spiral tracheids are 18/* in the one parent, 30 m in the 

 other, and 25 m in the hybrid. 



Sepals. — The large superior (in position) sepal is a specially instructive study from 

 the standpoint of hair formation. That of C. Spicerianum has the halves strongly re- 

 flexed so as in many cases nearly to meet behind ; it is of a dull stone-white colour 

 except along the midrib, where is a slight amount of purple-red pigment. That of 

 C. insigne is flat or slightly arched inwards, of a pure white colour at the sides, but 

 the middle area is varied by numerous large purple-black spots distributed over a 

 greenish -white background. The hybrid exhibits a slight reflexion of the halves, has 

 the white lateral parts of each parent, and the spots of the latter, but these are lighter 

 in tint and usually smaller in size. 



Except where otherwise mentioned, the size and outline of the cells agree in the three. 

 In C. Spicerianum the margin is fringed by many glandular hairs like those described 

 above, but very few are found over the outer surface, where simple multicellular hairs 

 are most abundant. In C. insigne simple hairs of five to six cells not only fringe the 

 margin, but are copiously distributed over the outer surface, along with a few glandular 

 hairs. In the hybrid simple and glandular hairs are equally abundant round the 

 margin, and the first also occur over the exterior along with a few of the latter. The 

 inner sepal surface of C. Spicerianum is copiously and uniformly beset with gland- 

 tipped hairs, which in all cases spring from colourless cells of the epidermis, but have 

 some or all of their cells often filled with a rich ruby pigment, the presence of which in 

 the hairs gives the dull stone colour to the sepal. In C. insigne there is a rather scant 

 distribution of simple hairs, except over the dark purple spots which are quite glabrous. 

 In the hybrid a few simple hairs are inherited from the latter parent, but there is an 



1. Cypripedium 



Spicerianum. 



2. Cypripedium 



Leeanum. 



3. Cypripedium 



insigne. 



