INTRODUCTION 



THE study of morphology received a new impetus from 

 the works of Hofmeister and of Darwin, which appeared 

 just before the opening of the period under review. They 

 altered very materially the points of view from which 

 such study was undertaken, bringing two new principles 

 prominently forward. The researches of Hofmeister led 

 immediately to a conception of one uniform plan under- 

 lying the whole of the vegetable kingdom and so modifying 

 the old distinction between Cryptogams and Phanero- 

 gams. The modifications of such a fundamental unity which 

 could be traced in the several groups had, further, neces- 

 sarily to be studied in the light of Darwin's theory, and 

 adaptation came to be recognized as playing a very 

 prominent part in morphological problems. The alternation 

 of generations traced by him in the vascular Cryptogams 

 bulked large in the study of the time, and efforts, which 

 became gradually successful, were applied to tracing 

 it in the life-histories of the Gymnosperms and Angio- 

 sperms. The study and comparison of numerous forms 

 brought to light the curious continuous retrogression in 

 importance of the gametophyte and the corresponding 

 advances in magnitude and complexity of the sporophyte, 

 up to their culmination in the Angiosperms. A still further 

 development of this line of research raised the question 

 of the origin of the terrestrial flora and its relation to the 

 aquatic organisms from which its descent became gradually 

 more and more apparent. 



The theory of metamorphosis was shaken to some extent 

 by these studies, and especially by the pronouncement of 

 morphologists whose researches led them to the opinion 



