BOTANICAL EVOLUTION. 463 
Early Dicotyledons. 
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Apetale. TVhalamiflore.  Disciflore. Calyciflorz. Carolliflorze. 
The basis of this classification which is now pretty generally adopted 
is undoubtedly the correct one, viz., the relationship of plants as 
shown by their descent, but practically it is often somewhat difficult 
to place a given plant satisfactorily. And one of the chief difficulties 
arises from the fact that development is not always upwards, i.e., 
tending towards differentiation of organs and functions, but is 
equally often retrograde. I will give an example of this even at risk 
of being a little tedious. The common chickweed is furnished with 
five green sepals, five deeply divided white petals, ten stamens, and a 
pistil formed of three united carpels. Small and insignificant as the 
flower may appear to us, it is evidently attractive to certain insects, as 
may be seen by its bright little petals which open wide in the sunlight 
and by the little beads of glistening nectar which are produced round. 
the base of the stamens. From its own structure and that of most of 
its allies, we unhesitatingly class it among the Thalamiflore. But 
frequently when flowering in winter as it often does, chickweed 
produces no petals, and this for the simple reason that there are no 
insects to see it. And were we to see our little plant in winter, and 
without considering its allies or its summer flowers, were to proceed 
to classify it, we would probably put it among the Apetale. Now 
this very apetalous condition which our chickweed assumes at the 
season when no insects are about, has been permanently assumed by 
a genus of antarctic chickweeds, called from their want of petals 
Colobanthus, literally ‘‘mutilated flower,” and of which we have some 
five species in and around New Zealand. And this genus, as far as 
its petals are concerned, ought certainly to be classed among the 
Apetalz, were it not manifest from other characters that the plants 
forming it are modified chickweeds, and therefore belong to the 
Thalamiflore. A little,further off in relationship stands a whole 
group of plants constituting the natural order Paronychiew. Most 
systematic botanists place this order of flowers among the Apctale 
on account of the persistent want of petals, but anyone looking at its 
characters with the eye of the evolutionist and noticing its manifest 
relationship to the order to which chickweeds belong would consider 
it simply as a degraded offshoot of thelatter order, and would place 
it accordingly in the Thalamiflore. And in one of his latest works— 
the “Student’s Flora of the British Islands,”’—I notice that Sir J. D. 
Hooker places the two orders together. 
Among Monocotyledons it is a more difficult matter to trace the 
earliest forms which became differentiated. But it would seem that 
the first of them were flowers furnished with three carpels in the 
centre surrounded by whorls of stamens arranged also in threes. Of 
these the two outer rows gradually became modified into petals, and 
it is probable that all existing Monocotyledons are descended from this . 
primitive type, in which there were six petals, three or six stamens, 
