202 Comparative Physiology. 



togamia and Endogens are connected through Rhizantheae, which 

 resemble the former, but have spiral vessels like the latter. 

 Endogensj again, are connected with Exogens by the Coniferse, 

 which have the vessels distributed in a manner approaching the 

 Endogens in some, and, from the want of perfect spiral vessels 

 in others, approach the cryptogamous lycopodiums. 



On the question whether the lower plants, as fungi, are de- 

 veloped from distinct germs, or generated by processes antecedent 

 to their formation, by what has been called spontaneous gene- 

 ration, he says : " the infinite number of sporules the fungi pro- 

 duce, stated by Fries as ten millions from a single individual, 

 so subtle as scarcely to be perceptible, and so light as to be 

 raised by evaporation, and dispersed in so many ways by attrac- 

 tion, insects, wind, elasticity, &c., renders it difficult to conceive 

 a place from which they can be excluded. The germs thus 

 constantly floating in the atmosphere are developed according 

 as the nature of the decomposing matter they alight on is re- 

 spectively adapted to each, showing why certain kinds are 

 always found in certain situations." In the fungi found on 

 roots it is still more curious how each is adapted, and to be 

 found in the several situations. No sooner are the roots pro- 

 truded from some plants, than their own peculiar fungi are to 

 be found on each, and nourished by the peculiar excretions of 

 the roots. " The same germ may, however, assume widely 

 different forms, according to the circumstances which influence 

 its developement ; and it would seem the absolute number of 

 species among fungi is not nearly as great as has been usually 

 supposed ; and that the kind produced by a decomposing in- 

 fusion, or a bed of decaying solid matter, will depend as much 

 upon the influence of the material employed as upon the germ 

 itself which is the subject of it." On this head he quotes 

 the great number of species, and even genera, which have 

 now been found, by Fries and others, to be only diflerent 

 states of the same species; and the appearance of diflerent 

 species in fluids, in Dutrochet's experiments, according as 

 acids or alkalies were added. This subject is again re- 

 sumed in the chapter on Reproduction; it is to be wished, 

 however, that such variations should rather be referred to in- 

 completeness in the characters of species by the botanist who 

 first named them, than to any uncertainty in the develo]3ement 

 of germs, which savours too much of equivocal generation, and, 

 if once admitted, might tend to confusion. There are so many 

 ways of one germ being substituted for another, and it is so 

 nearly impossible to guard against this, and the variations of 

 species are so apt to be classed as distinct species even in the 

 higher plants, that the facts observed may be resolved perhaps 

 better into these than any other. 



