70 INTRODUCTION TO CTIYPTOGAMIC BOTANY. 



tint of Phaenogams, are generally very simple in their structure, and of 

 these the species which are most fruticose in habit, as Caulerpa, consist 

 of a single cell, however large and complicated the plant may be. In 

 some of the finer Algfe alone, organs exist, comparable with leaves for 

 their nervation and expansion. The prothallus, when produced, ends 

 in the formation of spores, analogous with pollen grains, and with the 

 spores of Acrogens, and homologous with the sporophores of Hymeno- 

 mycetous Fungi. The embryo cell in the more typical Acrogens gives 

 rise to an analogue of the embryo in Phtenogams, but in the less typical, 

 in which there is no prothallus, to fruit analogous with stamens. The 

 produce of the spores, though themselves generated after the same 

 type, is 80 different, that all comparisons are attended with great diffi- 

 culties. 



