40 



(43) whi^h "bears rhizoids; a colorle&s parenchyma free from in- 

 terstices , the cells of which have in part slightly re- 

 riculated and thickened walls; an assimilatory parenchyma 

 and an upper epidermis, broken through by breathing pores. 

 This complicated structure is almost entirely lost in speci- 

 mens cultivated in weak light or in rooms saturated with 

 vapor. The assimilatory threads, lying under the epidermis 

 of the upper side, and the thick-walled parenchyma cells 

 diaappear entirely; the thallus is composed in all its parts 

 of similarly formed cells; small amounts of chlorophyll may 

 be found in all the layers, in a superficial position some- 

 what more abundnatly than in a more deMal one* (Compare 

 fig. 10, right.) ■*■ 



Various other interesting examples might still be 

 ohosea from the list of Bryophytes, of which Ikvirill here 

 name only two. In "Bryum argent eum the cells in the Uf- 

 ?12 fASB ef fHg IBAves dies and fill with air, thereby 

 giving a characteristic silver sheen to the shoots. As 

 Gobel has proved,^ this differentiation of the leaf is 

 lacking v/hen the moss is cultivated in a damp 'place ; _ 

 the cells of the leaf apex remain alive and green. This 

 differentiation, originating through the dying off of 

 certain cell groups, is found also in other m,9ss varie- 

 ties and may be suppressed in them (Compare Gobel) 

 Leucobrytiin glaucum retains its structure, even when it 

 is cultivated under water. Oehlmann^ observed, further 

 a lack of differentiation in the "rudimentary leaves _ 

 of Sphagnum which he obtained by cultivating the moss m 

 poor nutritive media and with weak exposure to l^Sj t « 

 Y^ile normal leaves are composed of small green and large 

 cplorless cells, both kinds of cells are about equally 

 large in the rudimentary leaves and also arranged es- 

 sentially different from those in the normal leaf. AS 

 a matter of course, entirely similar phenomena of arrest- 

 ment may appear also in the richly differentiated tissue 

 of many Euthallophyte groups; marine algae furnish lav- 

 orable material^, especially those specimens which are 



1. Stahl, loc. cit. Huge, Beitr. z. Kenntn. d. veg. Org, 

 d. Lebermoose, Flora, 1893, Bd. LXXVII, p. 294. Beauverie Etude 

 d. modific. morph. et. anat. de thalles de Mar chant iaet de lu- 

 nularia obtenues experimentalement . Soc. Linn. Lyon 1898, i. a*m. 

 p. 57, Gobel. Organographie, 19.01, p. 301, etc. 



3. Ueb. d, Einfl, dl. Lichtes auf. d. Gestaltung der Kak- 

 teen u. and Pfl, Flora, 18.96, Bd. LZXXII . p. 1. Further Organ- 

 ographie, p. 368. Compare also Geneau De Lamarliere and Maneu, o. 

 Sur le flore des mousses des cavernes. C. R. Acad. Sc. Pans, 

 1901, .T. CXXII, p. 921. 



3. Yeget. Fortpfl. d. Sphagnaceen etc. Dissertation Frei- 

 burg i. Schw, 1898. 



4. Compare for example, Peterson. Note s. 1. crampons chez 

 le laminaria saccharina.i Bot. Not,, Bd. XXI, p. 319. 



