80 JouKXAL OF THE MiTCHELL SociETY \^8epfemher 



were of value in overcoming another serious difficulty — namely, the 

 fact that fertilized eggs remain attached to the parent plant for many 

 hours and perhaps days. This will be referred to later. 



Selected individuals were then transferred to aquaria of sea-water 

 which had been filtered in order to remove any chance reproductive 

 bodies. Oyster shells previously scrubbed and dried were placed in 

 the aquaria beneath the plants. Upon these the eggs and spores set- 

 tled in great abundance and immediately germinated. This was 

 found to be true of the eggs whether males had been put in with the 

 females or not — a clear case, it would seem, of parthenogenetic germi- 

 nation. In ever}' case there was a liberal growth of young plants 

 before the shells were transferred to the sea. The cultures were kept 

 in the laboratory for different periods of time, varying from four to 

 twenty-four days, occasionally changing the filtered water upon them. 

 Laboratory conditions within the above given time limits seemed to 

 have had no adverse effect upon them except that growth was less 

 rapid than when they were in natural surroundings. 



Incidentally, measurements of length were made when these cul- 

 tures were studied. The greatest length attained by any of the plants 

 is given in a separate column in most of the tables. By comparison 

 of the date on which the experiment was begun with the date of col- 

 lection an approximate idea of the rate of growth may be gotten. In 

 the first 50 days the best plants reach about 40 mm. in length, thus 

 attaining something less than an average of a millimeter a day. In 

 the next 30 days they frequently increase to 100 mm., thus averaging 

 about 2 mm. per day. Approximate measurements made* on selected 

 plants growing normalh- on the rocks confirm this result. 



A total of 63 such cultures were prepared and planted during this 

 summer, 22 derived from tetrasporic plants, 22 from males and 

 females, and 19 from female plants alone. In order to avoid contami- 

 nation from chance spores these cultures were generally planted in 

 regions at some distance from those in which Padina grew normally. 

 Unfortunately, as was subsequently found, the conditions of growth 

 are exacting, and consequently but few cultures matured their plants, 

 and these in but small numbers. For the sake of brcvitv. and in view 



