i 
The Leaf-skin Theory of the Stem: A Consideration 
of certain Anatomico-physiological Relations in the 
Spermophyte Shoot . 1 
EDITH R. SAUNDERS, 
Fellow of Newnham College , Cambridge. 
With thirty-four Figures in the Text. 
i. Introduction. 
( i) ^ 1 'HE original problem and the wider question which arose out of it. 
JL In the course of investigations upon the inheritance of hairiness 
in Matthiola incana , necessitating examination of the young plant from 
the moment at which the plumule becomes visible, one cannot but be struck 
with the remarkably sharp line of demarcation, occurring at the cotyledon 
node, between the completely glabrous hypocotyl and the felt-covered plumule 
(see Fig. i). As the shoot elongates it becomes apparent that the epicotyl 
axis is thickly covered with hairs as well as the foliage leaves, while the 
now fully developed cotyledons and hypocotyl remain glabrous (see Fig. 2 ). 
Confronted year after year with this sharp contrast one was inevitably led 
to speculate as to its cause. A study of many Spermophyte seedlings has 
brought to light certain anatomical and physiological relations which appear 
not only to furnish a clue to the different character of the axis above and 
below the cotyledon node, so conspicuous in many species besides the 
Stock, but to throw light on the nature of the shoot axis in general. 
(ii) The nature of the evidence. The observations from which the 
conclusions set forth below are derived are concerned almost wholly with 
the surface anatomy of the plant. They deal with relations some of which 
have been recognized and find mention in detailed systematic descriptions, 
although no particular significance seems to have been attached to them. 
Others, on the contrary, do not appear to have been noticed. Regarded by 
themselves and apart from all other considerations the anatomical features 
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1 A brief preliminary communication on this subject was made at the Meeting of the British 
Association for the Advancement of Science in 1921. The present account covers a much wider 
field of observation, and the application of the leaf-skin conception is considerably extended. 
[Annals of Botany, Vol. XXXVI. No. CXLII. April, 1922.] 
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