I50 Rhodora [Jurv 
the petiolules, so that the leaflets remain duting sleep with their apices 
pointing toward the zenith. Darwin regarded this as probably due to 
the resumption of a primordial habit inherited from a remote ancestor 
allied to and sleeping like a Trifolium.! 
The word “ reversion ” commonly means to us the reappearance of 
a Jong-/osf character, or at least of some peculiarity which has jumped 
one or two, or a few generations. But there is no essential difference 
between reversions in this restricted sense, and the ordinary reproduc- 
tion, without intermission, of the racial likeness from generation to 
generation. All the features of the adult, as regards form, color, ec 
are at each generation absolutely obliterated in the first, or unicellular, 
stage of the offspring. No length of years or passing of generations 
could make the obliteration more complete. The gap between the 
perfected parent form and the unicellular offspring is one compared 
with which the transition from the zebra-horse to the modern species is 
trifling. When the multitudinous peculiarities of form, color, tempera- 
ment, action, of structure external and internal, survive the plunge and 
come safely through one such down-sinking of the organization, there 
is little increase of wonder — as there is no difference in the essential 
process — when one or another of these peculiarities delays a little in 
coming to light again, under the form of what we call a reversion. 
Again, we think of reversions as characters that become fixed in 
the individual, when they appear. ‘The reverting pigeon permanently 
retains its slate-colored plumage, the reverting sheep its dun-colored 
or black fleece. In plants a reversionary leaf is a matured-leaf — it 
may be on an immature plant — differing from the ** full character ” 
leaf, and owing its form to the revival — as we say — of an ancestral 
impulse. But it is a familiar story that in the history of any living 
thing an orderly series of figures from the past appears, transient re- 
vivings of old groups, — systematized reversions. The phenomena of 
inheritance are all of one sort, whether the reappearing traits are per- 
manent or not, and whether they occur regularly or only occasionally. 
In the development of any individual we have thrown before us 
dissolving views of extinct, precedent races; views for the most part 
indifferently focused, but clear enough to give us most important infor- 
mation of the natural affinities, along old lines, of the developing form. 
In both branches of biological science this has, of course, long been 
recognized, and studies of development have been most fruitful. Both 
1 The Power of Movement in Plants, p. 347. 
