INTRODUCTION. XXV 



Rhodosperraeae, where both stems and leaves are often 

 composed of a homogeneous mass of such cells packed to- 

 gether. 



In fructification we find many modifications of struc- 

 ture, without much real difference either in the manner in 

 which the fruit is perfected or in the spore that is produced. 

 The spore that is finally formed in all the Alga3 appears 

 pretty nearly to agree in structure, and to consist of a single 

 cell or bag of membrane, filled with a very dense and dark 

 coloured granular or semifluid mass, called the eiulochrome. 

 This spore, on germination, produces a perfect plant, re- 

 sembling that from which it sprung. Nothing at all resem- 

 bling floral organs has been noticed in any, and all that 

 we know of the fructification is, that it takes place with 

 regularity, arising from the same parts of the frond, and 

 having the same appearance in plants of the same kind. 

 Its growth maybe watched from the commencement, when 

 the germ of the future spore begins to swell. But little 

 has been ascertained that throws light on the process of 

 fecundation. In some instances, it is true, as for example 

 in Zygnema, the spore is formed from the union of the 

 matter contained in a cell of one filament with that in a 

 cell of another, and it has been observed that the cells of 

 one filament uniformly give out, and that those of another 

 uniformly receive; but before conjugation no difference 

 whatever can be perceived between the two filaments. 

 This, which occurs in a tribe of very low organization, af- 

 fords the nearest analogy that has yet been noticed with 

 what takes place in higher plants. If it have any real 

 affinity with that process, we may fairly expect the disco- 

 very of sexes in the more perfect tribes ; and the seeming 

 analogues of male flowers have indeed been noticed in 

 some of these. Old authors invested the air-vessels of 

 Fiicus, or the tufts of hairs that clothe the surface of some 



