READINESS TO CHANGE 45 
the striae. In numerous examples seen such differences seem 
fairly constant within their species. 
PLASTICITY OF CHARACTERS 
Comparative readiness of characters to change, under exposure 
to changed conditions, especially of sun, shade or soil, seems to 
rank in about this order: 
Ist. Size and vigor of whole plant and of parts. First to change. 
2d. Number of heads. 
3d. Amount of pubescence. 
4th. Direction and angle of branching. 
5th. Thickness of leaf. 
6th. Roughness of leaf. 
7th. Depth of color of rays. 
8th. Rigidity or weakness and consequent attitude of stem. 
9th. Bracts. 
roth. Glands. 
11th. Leaf-form ; last to change. 
But some varieties have their idiosyncrasies respecting such 
changes, and transpose parts of this order; as A. macrophyllus 
pinguifolius, which seems to be particularly susceptible to influ- 
ence as to roughness and then as to size of leaf. 
PRIMORDIAL-LEAVES AS CLUE TO ANCESTRAL LEAF-FORM 
Can we read traces of the past history of Aster species in their 
succession of leaves? Does the growth-impulse as it develops 
one form of leaf after another on an uprising aster shoot, still pass 
through some of the ancestral stages? Do some of the numerous 
radical leaf-forms recapitulate for us in little the past history of 
their race? The radical series is quite uniformly begun by an 
entirely different shape from those following, entire and spatulate 
in narrow-leaved species, subentire and nearly circular in the 
broad-leaved. If we may see in this primordial leaf an evidence of 
the leaf-type borne by progenitors of the asters, we may con- 
clude that the development since has been in the line of produc- 
tion of cordation, acumination and serration, 7. e., developing the 
large serrate cordate acuminate leaves of the present time. If it 
could be proved that this primordial leaf holds true phylogenetic 
