.REPRODUCTION 261 



sexual reproduction were the more successful mode of repro- 

 duction, would its relative importance be so greatly reduced 

 among higher organisms, both plants and animals? Yet 

 what the advantages of sexual over non-sexual reproduction 

 are, is by no means certain. 



Between animals and plants there are striking resem- 

 blances in the processes which constitute and succeed sexual 

 reproduction. Fertilization and the formation of new indi- 

 viduals are the same in the two kingdoms, and the care of 

 the young between the times of their conception in the body 

 of the mother and of their separation from it also cor- 

 respond. Only among the highest animals, the Mammalia, 

 is the care of the offspring carried beyond what is found 

 among plants. The plant-mother cannot nourish her off- 

 spring after it has been separated from her body, though she 

 has supplied it with a store of food. The mammalian mother 

 can and does. This difference of degree in development 

 does not, however, make our comparison less suggestive. 



One point more needs emphasis in this connection. Since 

 the continuity of the species is the chief end of reproduction, 

 precautions to ensure its attainment must be taken. The 

 lower plants like the lower animals, simple in structure and 

 small in size, as a rule rely on the survival of some of their 

 numerous and but slightly developed offspring rather than 

 upon the better equipment of a smaller number of more 

 completely developed young. Among higher organisms, the 

 opposite is the general rule. The relatively small number of 

 the seeds of the Leguminosse, each seed containing a large, 

 well fed, and highly developed embryo, may be regarded as 

 typical of the higher plants, while the small, not fully de- 

 veloped embryos of the Orchidacese, Ericacese, etc., in the 

 seeds of which only small quantities of food are stored, 

 represent a distinctly lower type. 



There are two kinds of non-sexual reproduction, the vege- 

 tative and the spore. In the former a mass of tissue, capable 

 of carrying on many functions and of developing into a new 

 plant, is separated from the single parent. In the latter, 

 a single cell or, at most, two cells together are cut off. 

 These, though formed sometimes by the cooperation of 



