INTRODUCTION TO CRYPTOGAMIC BOTANY. 168 



136. We have already had some approach to a simple frond- 

 like expansion in the genus Schizogoniwrn. Without, however, 

 adopting the notions adduced by Kiitzing, in his various works, 

 but more especially in his prize essay, on the origination of 

 these leaf-like expansions from ConfervcB, we have in the 

 genera Prasiola and Bangia, almost Confervoid threads, the 

 one representing the green, the other the purple series. If 

 the threads in these genera are laterally expanded by repeated 

 vertical division of the endochromes, it is evident that we shall 

 at once have a frond composed of one or more layers of cells, 

 not only elongated, but indefinitely expanded. In other cases, 

 instead of a flat expanded frond, a sac is formed, consisting of 

 a similar membrane, but closed all round, either for a season 

 only, or during the whole period of life, and branches of one 

 or many orders are formed from it by a process not dissimilar, 

 in all probability, from that by which the first sac was gene- 

 rated from the young spore. It is easy to conceive a scheme 

 for such a formation, but I am not aware that the mode of 

 growth has actually been followed out through every stage.* 

 The increase in this order very frequently takes place by the 

 quaternate division of the endochromes, especially in. the fresh 

 water species, and the frond often progresses for a long time 

 without any appearance of fruit. This, however, is formed by 

 an organisation of the granular matter of the endochromes, 

 and the resultant zoospores have two flagelliform appendages. 

 In Phycoseris gigantea, there are frequently four, as also in 

 Ulva bullosa. The biciliate spores, however, do not arise 

 precisely from the same tissue as the quadriciliate, but from 

 one consisting of smaller cells, and are themselves smaller. 

 The plants also which produce them have a yellow tiut.f The 

 young plants, on their first appearance, are in all respects sim- 

 ple Conferuce, but the apical cells soon divide, and a plane or 

 saccate frond is formed. 



137. M. Thuret informs us that he has seen the biciliate spores 

 germinate as well as the quadriciliate, which is certainly indi- 

 cative of identity of function. It is, however, right to men- 



* See, howevei-, Nageli neu. Algensyst., tab. 1, fig. 55 — 58. 

 t Thuret, 1. c. 

 11 * 



