156 



or exogenous and, according to this author, the cells of the short-celled filaments 

 are divided by intercalary divisions. 



The structure of the frond has been described in 1847 by N^geli (1. c). It 

 terminates in an apical cell which is said to be divided by oblique cell-walls pro- 

 ducing segments at all sides, and this is affirmed by Schmitz and Hauptfleisch 

 (Englei\ u. Prantl, Nat. Pflfam. 1,2 p. 517); it is however at least not general. The 

 young fronds arising from the basal disc have at all events an apical cell divided 

 by horizontal parallel walls, and this is also the case with young slender branches 

 (fig. 74, 6, C). In thicker shoots still in development I have found the segment walls 



somewhat inclined, but not 

 so much that they reached 

 the foregoing segment wall 

 (fig. 24, C). The cells of the 

 frond contain a single nu- 

 cleus and a number of disc- 

 shaped chromatophores. 



Some of the surface- 

 cells may produce a hya- 

 line hair of the same cha- 

 racter as in other Florideje 

 (fig. 74, D). In spring (March 

 to May) they are most devel- 

 oped, numerous, long and 

 rich in protoplasm; at 

 other seasons they are often 

 wanting. 



The frond is at first 

 cylindrical, but in an ad- 

 vanced age it becomes ir- 

 regularly compressed and 

 crisped (f. crispata Grev.). 

 In winter and in shaded 

 localities it is dark red-brown, while in sunny places in spring and summer it has 

 a light yellowish colour, the tips at last becoming green. 



The central cavity contains a thin slimy matter which seems to consist of 

 pectic substances; it forms a network in the cavity, the meshes containing probably 

 only water. 



The sporangia are, as is well known, immersed in the wall of the frond; they 

 are born of a cell in the inner cortex bearing moreover at least two cortical fila- 

 ments (comp. KuTZiNG Phyc. gen. tab. 74 II). The sporangium is connected through 

 a pit with the bearing cell but not with other of the cortical cells (fig. 74, E); thus 

 it is terminal and not intercalary as in Dilsea. The division is always cruciate; but 



Fig. 74. 



Diunontia incrassata. A, five days old plant from germinating letraspore 

 B, upper end ol side ))ranth showing transverse segment walls. C. lip of 

 yonng frond ; November), the segment walls in the main a.xis slightly inclined. 

 £), young hair. E, transverse section of frond showing a young sporangium. 

 F. transverse section of frond showing the develoiiment of the antheridia. 

 .1 300 : 1 . /}, C, E 390 : 1. D, F (330 : 1. 



