Ix REPORT — 1856. 



In like manner a curious correspondence has been traced between the 

 lower tribes of animals and plants, in the circumstance of both being subject 

 to the law of what is called alternate generation. This consists in a sort of 

 cycle of changes from one kind of being to another, which was first detected 

 in some of the lower tribes of animals, a pair of insects, for example, producing 

 a progeny differing from themselves in outward appearance and internal 

 structure, and these reproducing their kind without any renewed sexual union, 

 the progeny in these cases consisting of females only. At length, after a 

 succession of such generations, the offspring reverts to its primaeval type, and 

 pairs of male and female insects of the original form are reproduced, which 

 complete the cycle, by giving rise in their turn to a breed presenting the 

 same characters as those which belong to their own progenitors. 



An ingenious comparison had been instituted by Owen and others between 

 this alternation of generations in the animal, and the alternate production of 

 leaves and blossoms in the plant; but the researches to which 1 especially 

 allude have rendered this no longer a matter of mere speculation or inference, 

 inasmuch as they have shown the same thing to occur in Ferns, in Lyco- 

 podia, in Mosses, nay, even in the Confervas. 



We are indebted to Professor Henfrey for a valuable contribution to our 

 Transactions in 1851 on these subjects, given in the form of a Report on 

 the Higher Cryptogamous Plants ; from which it at least appears, that the 

 proofs of sexuality in the Cryptogamia rank in the same scale as to com- 

 pleteness, as those regarding flowering plants did before the access of the 

 pollen tubes to the ovule had been demonstrated. Indeed, if the observations 

 of Pringsheim with respect to certain of the Algae are to be relied upon, 

 the analogy between tiie reproductive process in plants and animals is even 

 more clearly made out in these lower tribes, than it is in those of higher 

 organization. 



It also appears, that the production in Ferns and other Acrogens of 

 what has been called a pro-embryo ; the evolution of antheridia and arche- 

 gonia, or of male and female organs, from the former; and the generation 

 from the archegonia of a frond bearing spores upon its under surface, is 

 analogous to what takes place in flowering plants in general ; where the seed, 

 when it germinates, produces stem, roots and leaves ; the stem for many gene- 

 rations gives rise to nothing but shoots like itself; until at length a flower 

 springs from it, which contains within itself for the most part the organs of 

 both sexes united, and therefore occasions the reproduction of the same seed 

 with which the chain of phsenomena commenced. This is the principle 

 which a learned Professor at Berlin has rather obscurely shadowed out in 

 his Treatise on the Rejuvenescence of Plants, and which may perhaps be re- 

 garded as one at least of the means, by which Nature provides for the stabi- 

 lity of the forms of organic life she has created, by imparting to each plant a 

 tendency to revert to the primaeval type. 



To the elder DeCandoUe we are also indebted for some of our most philo- 

 sophical views with respect to the laws which regulate the distribution of 

 plants over the globe, — yiews which have been developed and extended, but 

 by no means subverted, by the investigations of subsequent writers ; amongst 

 whom Sir Charles Lyell, in his ' Principles of Geology,' and the younger 

 DeCandolle, a worthy inheritor of his father's reputation, in his recently 

 published work on Botanical Geography, have especially signalized them- 

 selves. But it is to the late Professor Edward Forbes, and to Dr. Joseph 

 Hooker, that we have principally to attribute the removal of those anomalies, 

 which threw a certain degree of doubt upon the principles laid down by 



