380 Miscellaneous. 



scribing some new observations on the development of the micro- 

 spores of the higher Cryptogamia, the author endeavours to take in 

 at one view the whole series of phenomena of reproduction in the 

 higher plants ; and he shows how factitious are the old divisions, 

 and how much less marked than was formerly supposed are the 

 differences between one group and another. Without following him 

 precisely in the arguments which he finds in this in favour of the 

 theory of the filiation of types, we confine ourselves to regarding these 

 extremely interesting observations as fresh proofs of the unity of the 

 plan of creation. 



In the first part of his memoir M. Millardet investigates the ger- 

 mination of the microspores of the genera Marsilea, PUularia, 

 Isoetes, and Selaginella. He has ascertained throughout the presence 

 of a more or less developed prothaUium — a peculiarity which has 

 escaped all other observers. In the MaraUecB and PilidarlfP this 

 prothallium is represented physiologically rather than morphologi- 

 cally, if we may so speak. The antheridium, whilst becoming de- 

 veloped in the heart of the microspore, leaves aroimd it a space 

 filled with a mucilaginous liquid charged with nutritive substances. 

 Although no cell is to be found in them, these mateiials evidently 

 subserve the production of the antheridium, and thus play the part 

 of a true prothallium. In Isoetes and SclagineUa the prothallium, 

 although morphologically better defined, plays scarcely any physio- 

 logical part. The contents of the microspore, in fact, divide into 

 two parts, one of which, very much smaller than the other, a true 

 vegetative cell concealed in the apex of the microspore, becomes 

 enveloped by a membrane, and undergoes no subsequent metamor- 

 phosis. In the larger part, on the contrary, the antheridium is 

 developed, and this, in the former of these genera, gives origin to 

 four antherozoids only, whilst in the second it produces a much 

 larger number. 



As to the antherozoids, the author takes up a position opposed to 

 that of Schacht. He absolutely denies their cellidar nature, re- 

 gards them only as modified protoplasm, and shows that the vesicle 

 which often adheres to them has no physiological importance in the 

 act of fecundation, and, moreover, is very often wanting. According 

 to him, it is nothing bi;t the residue of the protoplasmic mass placed 

 at the centre of the mother cell, and at the expense of which the 

 antherozoid has been developed. 



In the second part of his work, M. Millardet, having ascertained 

 the existence of a male prothallium where none was known before 

 his researches, endeavours to bring forward the morphological im- 

 portance of this fact by sketching rapidly the evolution of the prin- 

 cipal types of the higher plants. As it has been expressed by M. 

 Sachs, we understand by alternation of generations, or alternant 

 generations, " the regular siiccession in the morphological cycle of 

 an individual of several completely diff'erent forms, derived from so 

 many profound changes in its mode of development." Resting 

 upon this difinition, the author shows successively, in the diff'erent 

 groups of the higher Cryptogamia and of the Phanerogamia, the 



