FUNCTION.] PERNS, ETC. 143 



autumn; the base of the flowering stem thickens, enlarges, 

 and assumes the appearance of a new corm ; in the spring, 

 leaves sprout forth, and elaborate matter enough to fill the 

 cells of the new corm with starch, and to organise another 

 oblique bud at the base ; the growth of a new individual is 

 then accomplished. In the meanwhile, the original corm is 

 exhausted of all its organisable contents, which are consumed 

 in the support of the young corm produced from its base ; 

 and, by the time that the growth of the latter is completed, 

 the mother is shrivelled up, and dies. It is easy to conceive 

 many modifications of this. 



Upon one or other of the two plans now explained are all 

 flowering plants developed ; but in flowerless plants it is dif- 

 ferent. In arborescent Ferns the stem consists of a cylinder 

 of hard sinuous plates, connected by parenchym, and sur- 

 rounding an axis, hollow, or filled up with solid matter. It 

 would seem, in these plants, as if the stem consisted of a mere 

 adhesion of the petioles of the leaves in a single row ; and that 

 the stem simply lengthens at the point, without transmitting 

 woody matter downwards. Some valuable observations upon 

 this point have been made by Mohl, who has, however, been 

 able only to investigate the anatomical condition of Tree Fern 

 stems, without studying their mode of growth. Lycopods 

 equally increase by simple addition to the point ; and, as this 

 seems also to be the plan upon which development takes place 

 in other cryptogamic plants, I have proposed the term Aero- 

 gens, to distinguish the latter from the classes of Exogens 

 and Endogens. 



When leaves are no longer formed, but growth takes place 

 by an irregular expansion of cellular tissue in various direc- 

 tions, the preceding rules are departed from, and nothing 

 being left of the vegetable fabric except the horizontal order 

 of growth, a stem ceases to appear, and a plant becomes 

 an unsymmetrical body, either consisting of solid masses 

 increasing in all directions, or of filamentous matter multi- 

 plying itself by internal septation at the elongated apex. 



