74 ERIGERON MUCRONATUM. POINTED ERIGERON. 



Erigcron miicrojiahim, the pointed- leaved Erigcroji, is well 

 adapted to illustrate both these divisions of botanical science. 



As regards the change of leaves to flowers, the manner varies 

 with different species. We like to refer to it in composite or 

 aster-like plants, for it is seldom that we proceed to trace it in 

 any one of them without learning much of the immense amount 

 of variety which nature works out of a few simple materials. It 

 may be remembered that there is not only growth in plants, but 

 that growth is in waves or rhythms, and that there is a suc- 

 cession of these waves — the degree only varying with the species. 

 In the present one, we see that the earliest leaves — those near 

 the root of the plant — are small, slender, and rather blunt. As 

 the growth-wave proceeds, it gathers force, the leaves become 

 larger, and, when at what we may term the maximum force of 

 the growth-wave, deeply lobed. As the force declines, the stems 

 become weaker and are long drawn out, the leaves becoming 

 again smaller, and resembling those at the base or beginning of 

 the movement. The growth-wave is nearly exhausted, and 

 growth almost at a stand-still, when a second and weaker wave 

 begins, and this has more spiral activity than the first, and 

 results in the general calyx of the compound flower, or Involu- 

 cre, as it is technically called, every scale of which is a changed 

 leaf. 



Only for the rapid torsion, and for the peculiar position as 

 under the second wave of growth, these now involucral scales 

 might have been leaves drawn out on a stem just as we see in 

 the earliest phase of growth. But a third distinct wave com- 

 mences when the flower Is to be formed, and the ray florets may 

 be compared with the little root-leaves forming the beginning of 

 the first wave as already noted. They are more slender, but 

 there is the same tendency to narrowing at the base, and to 

 obtuseness at the summits. It Is particularly interesting to 

 watch these phases of growth in living composite plants. The 

 actual rest between the several waves can in many cases be 

 noted, and often timed. 



