HEVUE BHYOLOCrOUE 73 



only be seen in the immediate vicinity of the initial-cells. Anothei* 

 interesting feature of the growing-point is the extraordinarily 

 rapid development of the rhizoids. Even at a distance of only 

 t^To ot three cells hehind and on either side of the actively 

 dividing initial-eel's, one finds cells which have grown out to 

 form long rhizoids with brown and thickened walls (Fig, 2, B.). * 

 In an ordinary sterile thallus, practically all the rhizoids are of 

 one kind, and are narrow (about 10 ^ in diameter), with thick 

 cell-walls. These rhizoids spring from the whole under surface 

 of the thallus, extending to tlie exiremc margins and, as stated 

 above, almost reaching Hie initial-cells of the growing-point 

 They show a marked tendency 1*0 pass inwards and backwards," 

 so as to reach the middle ot the thallus, where they form a loose 

 bundle which runs back longitudinally and frequently makes 

 the thallus appear at first sight to possess a definite brownish 

 midrib. Besides these narrow rhizoids there is a second kind, 

 developed in small numbers in a sterile plant, which are wider 

 (about 40 f/ in diameter) and have much ihinner, colourless walls. 

 These wide rhizoids are couliiu'd to the median portion of the 

 tliallus, and they grow directly downwards into the substratum, 

 where their ends frequently become branched (Fig. 2, E.). 



In the descriptions given by Huge* and by Stephanif it is 

 stated that the wide medJLin rhizoids have thicker walls than the 

 narrow marginal rhizoids. 



MvcoRmzA. — Nearly all the plants examined by the writer 

 showed a fairly definite zone of cells containing fungal hypha^, 

 and presenting the appearance of a mycorhiza, similar to that des- 

 cribed for Preissia. This zone is confined to the thicker median 

 portion of the thallus, and lies immediately above the ventral epi- 

 dermis (Fig. 2. A. D.). It consists of from two to four or five layers 

 of cells, and, in longitudinal sections, is seen to extend to within 

 a short distance of the growing-point in many cases. The fungal 

 hypha) are frequently observed traversing the wide, thin walled 

 rhizoids, but were never seen in the narrow, thick-walled ones- 

 Sometimes the hyplue enti r the ventral epidermis directly. They 

 branch freiruenllv and the branches sometimes anastomose. In 

 many of the cells hyplue were seen to end in spherical vesicles, 

 having thickened walls and dense granular contents. f 



*Loc. cil., p. 10. 

 t Loc. cit,, p. 352, 



t These fungal hyphae, bearing vesicles, were described and figured by 

 Gottsche (Ueber das Genus ilonoclea, Bot. Zeitung, 1858, p. SCO). 



