PULLULATION IN THE GENETIC CYCLE. 



have, therefore, this series represented by two terms 

 [ovum] polype, medusa ; while in Laomedea dichotoma it 

 is represented by three [ovum] polype, medusa, sporosac. 

 In Eudendrium the series stops with the production of a 

 sexual zooid, in the form of a medusa ; in Laomedea it goes 

 on through the non-sexual medusa-bud, until it finds its ter- 

 mination in the sexual sporosac of the latter."* 



But the course of pullulation is most usually interpolated, 

 after the general typical character of the species has been 

 first acquired in all respects, save the peculiarities of sex. 



3. In fact, the orthomorphic gemmation, already no- 

 ticed as one form of alternation, almost always runs on into 

 a continued course of pullulation, the result being either a 

 swarm of free zooids, as in the case of the Aphides, or else 

 a composite structure, like the polypidom of a zoophyte, or 

 the leafy stem of a plant. In the last mentioned case, the 

 seed, derived from the impregnated ovule, emits in germi- 

 nation the primary leaf- shoot of the plant ; but, in the ma- 

 jority of instances, before reproductive organs are formed, 

 this shoot produces leaf-buds, from which other leaf-shoots 

 are developed, and from these again others originating in 

 the same way, and so on, till at last that form is acquired 

 proverbially known as a vegetation. As Professor Braun 

 remarks, " only a small proportion of plants reach the goal of 

 the metamorphosis (blossom and fruit) in the first genera- 

 tion, the majority attain this term only in the second, third, 

 fourth, or sometimes not till the fifth generation of sprouts, ""f* 



* Annals of Nat. Hist., 3d Ser., IV., 368, note. 



f Rejuvenescence in Nature, (Henfrey's Translat., Ray Soc.), p. 32. 

 Braun recognizes three orders of gemmations Cataphyllary (root and bud- 

 scales, nieder-blatter) , euphyllary (leaf-shoots, laub -blatter}, and hypso- 

 phyllary (floral shoots, hoch-bldtter} . He holds also that when blossoms 

 are formed, they occur after a definite number of gemmations, very con- 

 stant in the same species, and frequently throughout a whole order. 



See also Dana in Silliman's American Journal of Science, Nov., 1850, 

 and the Annals of Nat. Hist., 2d Ser., VII., 348. 



