4 BIOLOGY 



phase of the progress of the one may serve as an indication of the 

 progress of the other. 



In the second place, to outline the progress of biology even from 

 the standpoint of botany is too large a subject to be included in the 

 grasp of any one man in such a way that he can recognize the move- 

 ments in his own experience. The general botanist no longer exists 

 except in name, and any general survey of botanical activity would 

 have to be a compilation rather than a contribution. With these lim- 

 itations, it becomes necessary for me to restrict myself largely to such 

 an outlook as is given by plant morphology, and even then to speak 

 only of those conclusions that come naturally to one in contact with 

 the morphology of vascular plants. And yet I believe that a history of 

 the development of the fundamental conceptions of plant morphology 

 may be taken as a fair illustration of what has been going on, not only 

 in botany in general, but also in biology. 



In the third place, the period included in this survey of plant mor- 

 phology need not extend beyond the middle of the last century, for at 

 least three reasons: (1) The earlier progress of the science has been 

 outlined by Sachs in his admirable History of Botany ; (2) modern 

 morphology finds its beginnings in a very real sense in the work of 

 Hofmeister; and (3) Darwin's theory of natural selection gave the 

 strong evolutionary impulse that it has felt ever since. 



My principal theme, therefore, is the development of morphological 

 conceptions as illustrated by plant morphology. 



It would be confusing to introduce the mass of details and the 

 names of investigators suggested by this subject. Nor would there be 

 any advantage in recording the changes of conceptions in reference to 

 the great variety of structures developed by the plant body and in re- 

 ference to their relation to one another. My purpose is to illustrate the 

 general change of attitude, the shifting of the point of view, in refer- 

 ence to plant organs, as knowledge has increased. No definite names 

 or dates can be cited, for the movement has been general and gradual, 

 developed out of common experience and proceeding from the back- 

 ground of accumulated knowledge. Disregarding the numerous pos- 

 sible subdivisions, the attitude of mind towards a plant organ during 

 the last half-century has presented three distinct phases. 



I. The Phase of the Mature Organ 



At the beginning of the period under consideration, the morpho- 

 logist concerned himself chiefly with completed organs, and an over- 

 shadowing rigid taxonomy compelled the idea of their classification. 

 A few theoretical types of organs had been selected, and all organs 

 were forced by the doctrine of metamorphosis to lie upon this Pro- 

 crustean bed. All parts of vascular plants, for example, were re- 



