1 889-] BOTANICAL GAZETTE. ^7 



a much higher order, and. approaching in their complexity of 

 structure, power of growth, and self-division, the lowest or- 

 ganisms themselves. This has already been pointed out by 

 Darwin, and if this be conceded, it obviously follows that 

 these particles are not identical with chemical molecules in 

 the proper sense of the word. The truth of this has perhaps 

 in some measure been felt by Elsberg and Haeckel when 

 they gave to the molecules, which represent hereditary char- 

 acters, the distinctive name of '* plastidules/' 



Some other authors, in particular Spencer and Weismann, 

 have avoided this fault, but they do not assume, with Dar- 

 win, that every separate hereditarv character of each or- 

 ganism is represented by a separate kind of living parti- 

 cles. They, on the contrary, suppose that the living mat- 

 ter from which an organism is developed consists of indi- 

 visible particles, each representing all hereditarv characters 

 of the species to which it belongs. It is certainly of much 

 importance that de Vries has clearly pointed out the exist- 

 ence of this difference, as it will lead to a better understand- 

 ing 



Spencer has called these particles " physiological units :" 



* 1 _ _ _ • _ _ i i .1 r , , * -_i _!_ a. _ m 



Weismann has given them the name of "ancestral plasmata 



(Ahnen-plasmen), and he has applied his views to the more 

 recent discoveries in cellular morphology- He is of opinion 

 that the ancestral plasmata have their seat in the nucleus of 

 the cell. 



Though in many respects differing from the foregoing 

 hypotheses, still Nageli's " idioplasma " also represents all 

 characters of the species. 



This is a common feature of all these hypotheses, and 

 their most important distinction from Darwin's pangenesis, 

 as here it is assumed that every organism contains multitudes 

 of different pan gens, each representing a separate hereditary 

 character, or as Darwin himself has expressed it: 4i an or- 

 ganic being is a microcosm — a little universe, formed of a 

 host of self-propagating organisms, inconceivably minute and 

 numerous as the stars in heaven." 



The question, which of these opposed views is nearest to 

 the truth, is amply discussed by the author, and almost the 

 whole first part of the book is devoted to it. 



First it is shown that the different and numerous heredi- 

 tary characters which a species displays are in many respects 

 independent of each other. To those who believe in the or- 

 igin of species by means of natural selection, it is obvious 



