212 THE INDUCTIONS OF BIOLOGY. 



be conveniently so distinguished from other plants, the axis 

 which shoots up from the seed, and substantially constitutes 

 the plant, does not itself flower and bear seed ; but gives lateral 

 origin to flowering, or seed -bearing, axes. Though in uni- 

 axial plants, the fructifying apparatus appears to be at the end 

 of the primary, vertical axis; yet dissection shows that, 

 morphologically considered, each fructifying axis is usually 

 an offspring from the primary axis. There arises from the seed, 

 a sexless individual, from which spring by gemmation, in- 

 dividuals having reproductive organs ; and from these there 

 result fertilized germs or seeds, that give rise to sexless 

 individuals. That is to say, gamogenesis and agamogenesis 

 alternate : the peculiarity being, that the sexual individu- 

 als arise from the sexless ones by continuous development. 

 The Salpa show us an allied form of heterogenesis in 

 the animal kingdom. Individuals developed from fertilized 

 ova, instead of themselves producing fertilized ova, produce, 

 by gemmation, strings of individuals ; from which fertilized 

 ova again originate. In multiaxial plants, we have 



a succession of generations represented by the series A, B, 

 B, B, &c., A, B, B, B, &c. Supposing A to be a flowering 

 axis, or sexual individual ; then, from any fertilized germ it 

 casts off, there grows up a sexless individual, B ; from this 

 there bud-out other sexless individuals, B ; and so on for 

 generations more or less numerous ; until at length, from 

 some of these sexless individuals, there bud-out seed-bearing 

 individuals of the original form A. Branched herbs, 

 shrubs, and trees, exhibit this form of heterogenesis : the 

 successive generations of sexless individuals thus produced, 

 being in most cases continuously developed, or aggregated 

 into a compound individual ; but being in some cases dis- 

 coiitinuously developed. Among animals, a kind of hetero- 

 genesis represented by the same succession of letters, occurs 

 in such compound polypes as the Sertularia; and in 

 those of the Hydrozoa which assume alternately the poly- 

 poid form, and the form of the Medusa : the chief differences 



