7 8 COMMON LI VER WOR T. 



consist of rounded grains of protoplasm in which the 

 chlorophyll proper is contained, the protoplasmic body 

 being readily seen after the pigment has been extracted 

 by alcohol. Such grains are scattered throughout the 

 thallus, but are only effectively developed in special 

 cells, which arise from the floor of cavities formed by 

 depressions in the surface of the thallus, and which are 

 overarched by the epidermis at a very early stage of 

 growth. 9 Communication with the outside air is 

 secured by means of peculiar and highly developed 

 stomata. 10 They are wider in the middle than at the 

 upper and lower openings, each stoma forming a small 

 air-chamber. The border to the outer opening is sharp 

 edged and immobile, while the inner one is formed of 

 inflated cells which act as regulators to the passage of 

 air and moisture. Altogether a very perfect arrange- 

 ment is thus made for the aeration of the chlorophyll 

 tissue without undue loss of moisture. 



The under surface of the stem is provided with copi- 

 ous hairs, those of the wingsdeveloped to give support, 11 

 toward which the internal thickenings and spiral con- 

 striction of the walls contribute, while those of the mid- 

 rib, larger, smooth-walled, and somewhat colored, serve 

 to fix the plant to the earth and to take up from it the 

 water and nutriment required, i. e. to perform the 

 office of roots. In a physiological point of view 



9 Leitgeb,Die Athemoffnungen cler Marchantiaceen, in Sitzber. d. k. k. 

 Akad. in Wien, Ixxxi, 1880. This differs from the older view which 

 ascribed the openings to a separation of the epidermis from the under 

 lying tissues. Sachs, Text-book ist and 2nd Eng. eds. 



10 Described and illustrated by Voigt, Beitrag zur vergleichenden 

 Anatomic der Marchantiaceen in Bot. Zeit., 1879, P- 7 2 9- 



11 According to Strasburger, Das botanische Practicum, p. 314. 



