1918] AlTERXATIOX A.XD PARXIIEXOGEiS'ESIS IN PaDIXA 81 



of the fact that iiuicli fuller data were secured in subsequent years, a 

 detailed report covering these cultures is omitted, as well as for the 

 summer of 1911, in Avhich the experiments were again begun, but 

 terminated before completion except in very small part by the writer's 

 unavoidable withdrawal from the laboratory. 



TETRASPOKES 



During the summer of 1912 the experiments were again duplicated. 

 For testing the product of tetrasporic plants, 4 series of 4 shells each 

 were prepared in the manner above described. Tlie cultures were 

 planted between the 29th of July and the 9th of Augiist. Since it 

 had been found, as above mentioned, that little or no growth occurred 

 except in places where Padina naturally thrived, cultures were 

 planted in such localities exclusively. The shells were secured at 

 different distances below the low-tide level to iron jjipes driven into 

 the sand. This was done with copper wire passed through holes 

 drilled in the shells and pipes. As but little growth had occurred by 

 the time it was necessary for the writer to leave the laboratory, a 

 return trip to collect them was made September 25th. They were 

 taken to Durham, X. C, in alcohol. By means of holes drilled in 

 the shells and notches filed on the edges every culture could be identi- 

 fied with absolute certainty. Every plant from these cultures was 

 examined with the compound microscope in order to determine with 

 positiveness the kind of reproductive body borne upon it. 



Of the 10 cultures covered with sporelings when planted, r» showed 

 no growth, 4 were not recovered, while the other 7 gave varying de- 

 grees of success. Table Xo. 1 gives the results and in part tiie con- 

 ditions of the experiment all tabulated in detail. The total result is 

 If)! males, i:]4 females, no tetrasporic, 2 doubtful, and 239 sterile 

 individuals of small size. The doubtful plants are so classified be-. 

 cause they have but few reproductive elements and these so young that 

 it could not certainly be told whether they were female or tetrasporic. 

 It should be stated, jx'rliaps, tliat feinal(^ and tetrasporic plants an-, 

 when young, often very similar in appc^arance, and in many cases even 

 when mature can be distiiiiiuished with (VM-laintv "nlv bx m.:.~nrr- 



