SEXUAL AND NON-SEXUAL REPRODUCTION. 



443 



1137. Contrast between non-sexual and sexual reproduction as 

 regards results. In non-sexual reproduction a certain portion 

 of living matter is separated from the rest of the living matter 

 of the plant, and, coming under favorable conditions, pursues 

 an independent existence ; in sexual reproduction, two portions 

 of living matter, from different parts of the organism or from 

 different organisms, unite to constitute a new individual. 



fern-spores. On a piece of unglazed earthenware, for instance a broken flower- 

 pot, which has been first boiled for a time in water to destroy any injurious 

 moulds, a few spores are to be lightly 

 dusted. If the whole is covered by a 

 bell-jar and kept dark and warm, after 

 a certain time the delicate films will be 

 detected and can then be traced through 

 their development. 



(7) Some of the allies of the ferns 

 produce spores of more than one sort, 

 differing in size and subsequent devel- 

 opment. The larger spores, known as 

 macrospores, give rise to an included 

 prothallus which subsequently becomes 

 exposed at one portion, where there is 

 developed an archegonium (or sometimes 

 more than one). Previous to or coin- 

 cident with this development there is 

 formed within the spore-walls a peculiar 

 tissue which has been termed the endo- 

 sperm, and which is regarded as the 

 homologue of the endosperm in gymno- 

 spermous seeds. The smaller spores are 

 denominated microspores, and pursue a 

 peculiar course of development. One 

 of the cells (seldom more than one) 

 remains essentially unchanged, while 



the others give rise to the mother-cells of the antherozoids. It is therefore 

 thought proper to consider the sterile cell as the homologue of a rudimentary 

 male prothallus, and the others of rudimentary antheridia. From the mother- 

 cells are produced, sooner or later, the antherozoids by which the archegonium 

 is fertilized. 



If these allies of the ferns are compared with the angiosperms, wide differ- 

 ences are found to exist which can be bridged over, in part at least, by the 

 gymnosperms. Hence, in some systems of classification the gymnosperms are 

 placed between the angiosperms and cryptogams instead of between the mono- 

 cotyledons and dicotyledons. 



Fig. 214. Selaginella. A, F, microspores in different stages of formation of the 

 antheridia G, antherozoid; H, axile longitudinal section of a macrospore six weeks 

 after fertilization, but before germination; v, rudimentary prothallus of the micro- 

 spore ; p, prothallus of the macrospore with three archegonia ; end, endosperm ; e, 

 exosporium. (Pfefier.) 



