PULLULATION IN THE GENETIC CYCLE. 1 41J 



have, therefore, this series represented by two terms — 

 [ovum] polype, medusa ; while in Laomedea dlclwtonm 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 g'emmation, 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. + 



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



t Rejuvenescence in Nature, (Henfrey's Trauslat., Ray Soc), p. 32. 

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

 scales, nieder-hldtterj , eupliyllary (leaf-shoots, lauh-hldUerJ, and hypso- 

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

 are formed, they occur after a definite number of gemraatioiis, verj' cou- 

 staut in the same species, and frequently throughout a wliolo order. 



See also Dana in Silliman's American Journal of Science, Nov., 185(1, 

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



