S76 THE WATTTEAL HISTOKT EEVIEW. 



tubular, pseudo-foliar, and pseudto-axial Thallogens, as the general 

 features of their composition are well known. 



Gaulerpa might have found a place in Mr. Spencer's digest as 

 having, though strictly a unicellular plant, a creeping stem, so to 

 speak, growing indefinitely and giving origin to two kinds of 

 branches of limited growth, viz. : roots on one side, leaf-like branches 

 on the other.* 



Lessonia, though merely an aggregate of the second order, has a 

 pseudo-foliar and pseudo-axial appearance. In Rhodymenia, Pliyllo- 

 phora, and Delesseria, there are successive stages in gradually in- 

 creasing complexity. In the last-named beautiful sea-weed there 

 are small fronds springing from the mid-rib of the parent frond, and 

 completely resembling it, except in size. This tertiary degree of 

 composition is yet more fully shown in Sargassum. 



In passing from Algae to Jungermannice, Mr. Spencer calls atten- 

 tion to the widely different circumstances under which terrestrial 

 plants are placed, as compared with aquatic ones, and the conse- 

 quent modifications in their mode of growth. The Jungermannice 

 exhibit transitional forms from aggregates of the second order to 

 those of the third order, till at length the more perfect of them 

 have an erect stem with separate leaves, and a single root or group 

 of roots ; so that the leaves are now not able of themselves to carry 

 on their functions, but depend one on another, and on the other 

 organs, and in this way make up a compound individual. 



Having thus dealt with flowerless plants, Mr. Spencer proceeds 

 to the consideration of the morphological constitution of flowering 

 plants, in which there is always aggregation of the third order, and 

 very frequently aggregations of the fourth, fifth, or sixth orders, Mr. 

 Spencer here using the word aggregations in the same sense a» 

 Alexander Braun does, when speaking of the "generations" of 

 shoots, &c. 



In speaking of the promulgation of the doctrine of metamor- 

 phosis, the principal merit is assigned justly to Wolff, for although 

 Goethe arrived at his conclusions independently, and by a partially 

 different road, " he is only entitled to a secondary place among those 

 who have established this important generalization." The consi- 

 deration of this subject leads Mr. Spencer to ask the important 

 questions, " What is a foliar organ, and what is an axial organ ?'* 



* Decaisne Plautes de I'Arabie heureuse. Arch, du Mas. ii. 1839. t. vi. B. 



