General Introduction 9 



sequence of relationship. By careful comparison of the 

 life- histories of the plants comprised in the four now familiar 

 principal divisions, he demonstrated a unity of plan appear- 

 ing through great differences of structure and development 

 a uniformity based upon the curious life-cycle known 

 to-day as the alternation of generations. Researches made 

 thenceforward till near the end of the period under review 

 showed that this uniformity and plan goes even further 

 than Hofmeister taught, and vindicated the attitude he 

 took and the great generalization associated with his name. 



The bearing of his work was thus twofold ; its morpho- 

 logical importance in pointing out the homologies of the 

 reproductive organs of Cryptogam and Phanerogam, and 

 its consequent explanation of the occurrence of that 

 feature forming a distinction between the two groups 

 the seed was perhaps even of less consequence than its 

 influence in emphasizing the new principle in classifica- 

 tion that resemblance in particular characters indicates 

 affinity based upon descent. Hofmeister developed the 

 idea of the descent of the highest plants from primitive 

 simple ancestors, and so struck a heavy blow at the dogma 

 of the constancy of species. 



The work of Hofmeister did not stand alone during those 

 years of patient inquiry. The researches of many others, 

 working on other lines, were similarly preparing the way 

 for that recognition of evolution in the organic world which 

 found its definite presentation in the writings of Darwin 

 and Wallace. A little prior to 1860 morphology was 

 studied in the light of theories of development and met 

 therein with a certain explanation. The^cell was recognized 

 as the unit of construction of all organized bodies, and the 

 study of its multiplication and development was a feature 

 of the time. The cell theory of Schleiden and Schwann 

 had obtained general acceptance, the work of Von Mohl 

 was exciting much interest and controversy, and the 



