. A compendium of general botany. Plants. 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 difterences 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 sjDermatozoids, wdiile on the other hand no micro- spore of a vascular cryptogam can develop a pollen-tube. 2. By comparing the phanerog
. A compendium of general botany. Plants. 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 difterences 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 sjDermatozoids, wdiile 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 diflerent. Among mosses the leafy plant develops from spores produced asexually, while among vascular cryptogams the plant proper is the jDroduct 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 ; 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 V. 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- ' Voilesungeu, p. 923. "^ Tbeorie der Abstammuugslehre, p. Please note that these images ar
Size: 1759px × 1420px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
