REPRODUCTION. 201 



idea; only the speculative fantasy of the theory of descent finds 

 it necessary to construct concrete connecting links between these 

 existing contrasts. 



In regard to the differences just mentioned, the following shall 

 now be mentioned, although the beginner will only comprehend the 

 subject fully from what will be stated later. 



1. No pollen -grain of a phanerogamic plant is capable of pro- 

 ducing motile spermatozoids, while on the other hand no micro- 

 spore of a vascular cryptogam can develop a pollen-tube. 



2. By comparing the phanerogams with viviparous animals, as 

 Sachs has done, we find that the contrast between vascular crypto- 

 gams and phanerogams is too great to enable us to compare the 

 vascular cryptogams with oviparous animals. This fact Sachs him- 

 self emphasized. ' 



3. Although the antheridia and archegonia of vascular crypto- 

 gams and leafy mosses resemble each other, it is evident that the 

 relative behavior of sexual and asexual generation is materially 

 different. Among mosses the leafy plant develops from spores 

 produced asexually, while among vascular cryptogams the plant 

 proper is the product of the fertilized egg- cell. NAGELI, the 

 shrewdest and most zealous supporter of the theory of descent, 

 supposes that the present phanerogams were derived from former, 

 now extinct, vascular cryptogams, and these from moss-like plants. 2 



We shall now enter more fully into the particulars of this com- 

 parative study. Let us suppose the entire development of a plant, 

 beginning with a reproductive cell and terminating with a cell of 

 equal value, to be represented upon a circle, as is shown in the 

 accompanying diagramatic sketch (Fig. 124, 1, 2). This shows 



FIG. 124. 



the relation between a moss and a fern. 1 Represents the moss 

 and 2 the fern ; G the sexual generation and U the asexual genera- 



1 Vorlesungeu, p. 922. 



2 Mech.-phys. Theorie der Abstauirnimgslehre, p. 472. 



