AlTEUXATIOX AXI) PAUTirF.XOflF.XKSlS IX Padixa 79 



plants and that tetraspores invariably produce male and female 

 plants. Since the present experiments were begun, Lewis (2) has 

 published the results of similar experiments upon several species of 

 Rhodophyceae ; his findings without exception confirming the theory 

 of alternation. 



Perhaps it may not be out of place in passing to point out that 

 these plants, together with the one now under discussion, furnish 

 teaching material peculiarly valuable in presenting the theory of 

 antithetic alternation of generations by reason of the fact that the 

 sporophyte is an entirely separate and distinct individual plant of 

 ecjual size and the same general ap]iearance as the gametophytes. 



During the summer of 11)10, while engaged at the Bureau of Fish- 

 eries' laboratory at Beaufort, ]^. C, in working on the morphology 

 and cytology of Padina, it occurred to the writer that it would be well 

 to duplicate Hoyt's work on Dictyota with this species. Further- 

 more, as it had been noticed that unfertilized eggs in laboratory cul- 

 tures x^roduce sporelings indistinguishable from those produced by 

 tetraspores and fertilized eggs, and, as algologists (4) were uncertain 

 as to whether or not fertilization was absolutely necessary in certain 

 of the Dictyotaceae, it was determined to include unfertilized eggs in 

 these experiments. 



To grow spores to maturity at the laboratory being impossible, the 

 method devised by Hoyt ( 1 ) was resorted to. Cultures were started 

 ill iitjuaria on oyster shells which were later transferred t<t various 

 ])laces in the harbor. 1'lie material to be used in these cultures when 

 brought to the laboratory was sorted with the compomid microscope, 

 males being put into one aquarium, females into another, and tetra- 

 sporic i)lants into a third. Pliey were kcj)t tlnis under runiiinu' water 

 for variable periods of time before the ex])eriments were bt^gun. This 

 was a precaution against transferring antherozoids in llie experiments 

 with mifertilized eggs, since, although there is a certain periodicity in 

 tlie production id' eggs and s|)ernis and. as i'-.w as im-siMe. material 

 was therefore collected on the day preceding maturity of si-xual ele- 

 nieiits, there are sometimes two or even tliree cro|>s of jintlieridia on a 

 plant at tlie -anie time. So far as sperms ure concerned tliis preeaiu- 

 tion proved unnecessary, luil very long periods of time ( -evcral days) 



