1018] Alternation and Parthenogenesis in Pabina 85 



female plant were put in each aquarium except series 5, in which 

 several males and females were used. Of the IG cultures thus ob- 

 tained from male and female plants ])lacod together in the same 

 aquarium, which it was for a while supposed certainly insured fer- 

 tilization, 5 only exhibited a tolerable growth. Fourteen of these 

 plants are females, 2 males, 14 tetrasporic, 3 doubtful, and 97 sterile. 

 We should expect only tetrasporic individuals, and we should expect 

 also much larger numbers, comparable to some extent with those 

 secured when tetrasporic plants were used as the source of the cul- 

 tures. The results are not markedly different from those obtained 

 when female plants without males were used as the source of the 

 spores (Table 3). 



The experiment was duplicated again in 1914 (Table 5) with 

 essentially the same result, except that a greater proportion of cul- 

 tures were successful and the number of plants per culture was 

 somewhat larger. Since the opportunity for foreign spores to settle 

 upon the cultures was somewhat greater by reason of the fact that 

 the shells were attached in the immediate vicinity of fruiting plants, 

 with their surfaces in the horizontal instead of the perpendicular, it 

 is now safe to conclude, especially in the light of the following experi- 

 ment, that most of these plants were derived from chance reproductive 

 bodies settling upon the shells rather than the supposedly fertilized 

 eggs which were germinating upon them when planted. It had pre- 

 viously been supposed that sperms would be freely discharged in tlie 

 quiet water of aquaria as are the eggs and tetraspores. An examina- 

 tion, however, of the water in which male plants had l)eon kept one 

 night showed the presence of but few sperms. It was then concluded 

 that the lacking factor for the discharge of sperms was probably tlie 

 constant activity of the s(>a in localities where Padina grew suc- 

 cessfully. 



Accordingly, in the summer of 1915 two series of experinieiifs 

 were devised to test this idea. The plants, male and iVmale, were 

 tied to supports so attached to ;in axle that they wen- alfernatdy 

 forced down into the water iind elevated a few iiiclns ;ib..vo at oM'h 

 rcvnlnfimi (Plate 1). 



