529 
the Gorse ( Ulex europaeus , L.). 
affected the average. Those omitted in the boxes of sand were more 
numerous, but, had they been included, they would no doubt have some- 
what increased the average difference between soil and sand, as the later 
countings (i. e. of backward seedlings) on sand gave low values for the 
number of compound leaves. 
In considering the result that the ancestral character is more pro- 
nounced on good soil, the suggestion may be made that this is a case of an 
ancestral character being favoured by ancestral soil conditions, since the 
gorse plant may be supposed to be descended from a plant with trifoliolate 
leaves, and having normal habitats among richer soil than that usually 
frequented by gorse. Other hypotheses expressed in terms of response to 
different physical factors might be attempted, but the above point of view 
should not be lost sight of, and may prove to have some theoretical 
importance. 1 
Lothelier 2 carried out some experiments in which, when gorse was 
grown in an atmosphere saturated with moisture, the spiny character of the 
plant disappeared, and the leaves became flat. Wollny, 3 however, found 
that only 13*5 per cent, of the plants of gorse with which he experimented 
gave the reaction described by Lothelier. Thus variation as regards 
plasticity has been recorded in gorse plants. 
It is quite possible that there may be also differences in plasticity as 
regards the number of compound leaves produced by the seedlings, some of 
the latter being more easily influenced by soil conditions than others. If 
this is so, the leaf characters of a seedling may be thought of, for the sake 
of clearness, in relation to theoretical normal conditions (as giving a fixed 
point). Then when conditions are other than normal, the actual number of 
compound leaves formed by a given seedling may be regarded as deter- 
mined by three factors, viz. (a) the number of compound leaves that would 
be produced by this individual under normal conditions ; (b) the degree of 
plasticity of this seedling ; (c) the deviation from normal conditions. 
For comparison with the result obtained with gorse seedlings, reference 
may be made to an experiment carried out some years ago on the garden 
wallflower. 4 In this case a presumably ancestral character was recognized 
in the three-armed hairs found on the early leaves of the seedling. These 
hairs were more numerous on seedlings grown on sand than on those grown 
on loam. 5 Thus the ancestral character is here more pronounced on poor 
1 See F. Darwin, Presidential Address, British Association, Dublin Meeting, 1908. 
2 Lothelier : Recherches sur les plantes a piquants. Revue Generate de Bot., vol. v, p. 519. 
3 Wollny, as quoted by Goebel, Experimentelle Morphologie der Pflanzen (1908), p. 35. 
4 Boodle : On the Occurrence of Different Types of Hair in the Wallflower. Ann. of Bot., 
vol. xxii, p. 714. 
5 Only forty seedlings were used in this experiment, so the result requires confirmation. Further 
experiments were begun, but were abandoned on account of the trying nature of extensive hair- 
counting. 
