150 Saunders . — The Leaf -skin Theory of the Stem: 
axillary buds develop in the vegetative region) and curves outwards and 
downwards on the side of the stem opposite that on which the hair line 
is formed in the internode immediately below. A well-marked line of hairs 
extends along the whole length of this flower axis on the inner (convex) 
side, i. e. the side which faces the geometrical centre of the whole system, 
and arises from the insertion of the posterior sepal whose edges lie outside 
its neighbours, and whose insertion width is so narrow that the two lines 
which we might expect to find apparently come into contact and form the 
single track which we see. On both the axillary axes which spring from 
the same node the hair line develops on the adaxial side, as has been 
described for the case of the lateral branches in the vegetative region. These 
relations have been observed also by Lundstrom , 1 who accounts for the 
suppression of the second line of hairs in the internode beneath the flower- 
ing node on the supposition that it would be useless in this position 
and hence is not formed. But this argument does not meet the case in the 
vegetative region. It would rather seem that hair formation is the outcome 
of a certain physiological condition which is not usually attained in the 
basal internodes, but is reached and maintained at higher levels, and may 
even now and aga,in exceed this normal limit and so lead to the formation 
of a second hair line. The direction of shift of the single line is not 
apparently predetermined, but is the result of a combination of causes 
affecting equilibrium at a particular moment. 
Upon comparing individuals growing in different situations, it becomes 
evident at once that the general uniformity of hair distribution characteristic 
of the axial surfaces is not manifested in the free region of the sepals, which 
varies greatly in degree of hairiness. In some plants the whole of the 
surface exposed in the unopened bud is hairy ; in other individuals it may 
be difficult to' find a single hair. But even though there be but one 
on the posterior sepal itself, the hair line marking the boundaries of its 
extension down the pedicel is as conspicuous as in those cases where the 
unopened bud is hairy all over. The production of hairs on the free surface 
of the sepal takes place in response to the particular conditions prevailing 
during the development of the axis, and has no hereditary significance. The 
hair line marking the boundaries of the sepal extensions is an inherited 
feature related to a definite morphological configuration, and makes its 
appearance as soon as the internode has an appreciable length. 
The general occurrence in Stellaria media of the single well-marked 
hair line in the internodes suggests (1) that an inequality of growth analogous 
to, if not identical with that which leads to the transition from an opposite 
to a spiral leaf-arrangement in so many, species, or which finds expression 
in the circumnutation of the shoot tip, is inherent or invariably becomes set up 
in this species ; (f) that this inequality is reflected along the lines of junction 
1 Nova Acta Reg. Soc. Sci. Upsaliensis, 1884. 
