136 Saunders . — The Leaf -skin Theory of the Stem: 
here described will seem, no doubt, trivial in character, but viewed in the 
light of their relation to the plan of construction as a whole they assume 
a new importance and call for some explanation capable of general 
application. The sought-for solution, simple and obvious when once the 
facts have been grasped, is to be found in a definite (? universal) downward 
extension of the leaf area below the node level. 
Figs. 1-6. 1, Matthiola incana, seedling showing glabrous cotyledons and hypocotyl and hairy 
plumule. 2, older stage (lower leaf-tips removed). 3, Veronica hederaefolia, seedling ; hypocotyl with 
a line of hairs along the potential edges of the cotyledon extensions. 4, Lopezia coronata , seedling 
plant ; hypocotyl and internodes showing the same feature. 5, Ipomoea sanguinea , young seedling ; 
a, the furrow formed between the edges of the cotyledon extensions. 6, older stage of the same. 
2. General Statement of the Facts and Consideration 
of their Significance. 
To return for a moment to the case of the Stock. It will be admitted 
that the absence of hairs from the cotyledons of a hairy-leaved form cannot 
be supposed to be entirely the result of an intra-seminal environment, since 
in some types the surface of the cotyledons is seen to be covered with hairs 
immediately they become free of the seed-coat. We need, therefore, to 
