2JkO BOTANICAL GAZETTE. 



plant in the Botanical Gardens at Cambridge, and for my own col- 

 lection, I was nnintentionally too good a collector, and probably ex- 

 tinguished the plant, though thinking enough had been left for seed. 

 Dr. Gray, on requesting the plants, said they were difficult to raise 

 from the seed, which may account for those left disappearing the 

 year after the first and second crop of specimens was reaped, there 

 being but few at the best. It grew on the gravelly banks of the 

 river, and it would be well for collectors to look for it in similar situ- 

 ations within the range above indicated, at least, with the precaution, 

 if found, of not cropping too closely, unless there is an "'abundance" 

 at Ottawa for all who may seek it personally or by exchange. — 



E. J. Hill, Englewood, III. 



Alternation of Generations. — A discussion of the subject of the 

 ''alternatiMi oi' generations'' in the Journal of Botany for November, 

 may be given in brief as follows: 



So far back as 1849, Hofmeister pointed out that the prothallium 

 of the Vascular Cryptogams is morphologically equivalent to the 

 moss-plant; that a Fern or a Lycopod is the homologue of the moss- 

 fruit; and further that in both Mosses and Ferns the asexual is in- 

 terrupted by a sexual reproduction, this interruption occurring at an 

 earlier stage in Ferns than in Mosses, and that the sexual and asexual 

 generation regularly alternate. 



So soon MS these views were generally accepted, attempts were 

 made to apply them to the life-histories of the Phanerogams on the 

 one hand and of the Thallophytes on the other. Such an application 

 is rendered difficult in the case of the former group, by the very in- 

 timate connexion of the two generations in the ovule, which makes 

 their exact distinction a matter of some uncertainty ; and in the case 

 of the latter group by the more or less complete independence of the 

 two generations and by the frequent repetition of the one before the 

 recurrence of the other. 



The generations of Thallophytes, like those of Cormophytes, begin 

 in all cases with a free cell, the spore, but unlike those of Cormo- 

 phytes, the generations are distinct and do not remain in organic con- 

 nexion ; consequently it is impossible to regard the "fruits" of Thal- 

 lophytes as representing an entire generation. 



The fact that such groups as the Conjugate and Fucacefe exist, 

 which exhibit no alternation of generations is presumptive evidence 

 against it. It seems to be more in accordance with the fact to say 

 simply that a sexual Thallophyte may reproduce itself either sexual- 



