;^82 THE JOUKNAIi OF JiUTANT 



conveniently indicated as the tetrasporopliyte, and is equally a 

 distinct ' generation ' or ' phase ' in the life-C3^cle. 



Such haploid spores, on immediate ' germination,' give a haploid 

 soma of normal free and autotrophic organization, which may he 

 sexual and repeat the sequence. But there is no reason at all why, 

 by omitting the sexual organs, it might not produce unilocular 

 sporangia, which being haploid would not require a meiotic division ; 

 and hence would not give a tetrad system, but 3'et ' spores ' of sorts 

 for free dispersal. Many decadent Floridean genera are in this 

 position, at the verge of latitudinal or vertical distribution ; as also in 

 many cases so-called tetraspores are found freely on the sexual 

 pla its K 



Special interest also attaches to cases in which the tetraspores are 

 wanting, as indicating the failure to produce meiotic sporangia ; and 

 the reducing-di vision has to be effected elsewhere. That the locus of 

 such a process is again wholly subsidiary and secondary is shown by 

 the details now available of cases in which the stages have been 

 followed. Thus in Scinaia, according to Svedelius (1915) ^, the 

 zygote divides meiotically to 4 nuclei, one of which is the parent 

 nucleus of the carposporophyte, Avhile the other three are rejected — a 

 method which recalls that of the transmigrant Sjjiro^i/ra^, and is 

 equally bad business, the expression of deterioration in organization, 

 since there is no compensator}^ gam. In JS'emalion, on the other 

 hand, according to Kylin (1916) * and Cleland (1919) •^, the zygote 

 nucleus divides, and a septum appears after the meiotic spindle, a 

 feature not known elsewhere ^ ; the meiotic tetrad is not completed, 

 and the homotype division of the basal segment does not follow^ 

 on, or is incomplete (Cleland). Such a variant on the meiotic 

 mechanism can again be only interpreted as evidence of deterioration 

 in the process, and the haploid sporophyte is thus quite a secondary 

 idea in the life-cycle of such forms, by cutting out a whole phase ; 

 so far affording an interesting light on the deterioration of this other- 

 Avise undoubtedly archaic type, left vestigial in Northern Seas, in 

 which again monoecism and autogamy are the normal rule for the 

 sexual plants 7. 



The clue to all i^eculiar behaviour on the part of the zygote and 

 young carposporophyte, in its relations to auxiliary cells, is seen in 

 its practically holoparasitic habit ; the idea being to pass as quickly 

 as possible to the nearest source of available food-supply (commonly 

 and most efficiently to the subtending cell of the carpogonial branch, 



^ In Gracilaria confervoides tetraspores, antheridia, carpogonial branches, 

 and cystocarps may all occur on the same individual. ' Tetraspores ' on sexual 

 plants are frequent in several species of Polysiplw7iia ; cf. Yamanouchi, Bot. Gaz. 

 (1906), p. 435. The cytology of these organs is so far unrecorded. 



2 Svedelius (1915), Nova Acta, Upsala, iv. p. 1. 



•^ Trondle (1911), Zeitsch. fiir Bot. iii. p. 593. 



"» Kylin (1916), Berichte, xxxiv. p. 257. 



•^ Cleland (1919), Annals Bot. p. 323. 



" C. Allen (1905), BeHchte, xxiii. p. 289, describes the full homotype divisions 

 in the first divisions of the zygote nucleus of the vestigial rather than incipient 

 siporophyte individual of Coleochsete. 



' Kylin (1916), loc. cit. p. 259, gives Nemalion as dioecious ; but the pre- 

 cocious production of antheridia is usual for small plants. 



