THE MORPHOLOGICAL COMPOSITION OP PLANTS. 75 



the colours assumed by these terminal folia, call to mind the 

 plants out of which we conclude that Phasnogams have been 

 evolved; for it is said of the fronds of the Jungermanniacece, 

 that, " though under certain circumstances of a pure green, 

 they are inclined to be shaded with red, purple, chocolate, or 

 other tints." 



As thus understood, then, the homologies among the parts 

 of the pha?nogamic axis are interpretable, not as due to a 

 needless adhesion to some typical form or fulfilment of a pre- 

 determined plan; but as the inevitable consequences of the 

 mode in which the phanogamic axis originates. 



197. And now it remains only to observe, in confirma- 

 tion of the foregoing synthesis, that it at once explains for us 

 various irregularities. When we see leaves sometimes pro- 

 ducing leaflets from their edges or extremities, we recognize 

 in the anomaly a resumption of -an original mode of growth : 

 fronds frequently do this. When we learn that a flowering 

 plant, as the Drosera intermedia, has been known to develop 

 a young plant from the surface of one of its leaves, we are at 

 once reminded of the proliferous growths and fructifying 

 organs in the Liverworts. The occasional production of bul- 

 bils by Phasnogams, ceases to be so surprising when we find 

 it to be habitual among the inferior Acrogens, and when we 

 see that it is but a repetition, on a higher stage, of that self- 

 detachment which is common among proliferously-produced 

 fronds. Nor are we any longer without a solution of that 

 transformation of foliar organs into axial organs, which not 

 uncommonly takes place. How this last irregularity of de- 

 velopment is to be accounted for, we will here pause a moment 

 to consider. Let us first glance at our data. 



The form of every organism, we have seen, must depend 

 on the structures of its physiological [or constitutional] 

 units. Any group of such units will tend to arrange itself 

 into the complete organism, if uncontrolled and placed in fit 

 conditions. Hence the development of fertilized germs; and 



