196 PHYSIOLOGY OF NUTRITION. 



74. Absorption of Water by Mosses. 



Mosses possess not true roots, but rhizoids. To acquaint our- 

 selves accurately with these organs we select Bryum csespiticium, 

 a moss which is frequently met with on moors. Soil clinging to 

 the plants is removed as completely as possible by means of a 

 stream of water. The lower part of the stem is cut off, trans- 

 ferred to a slide, and examined. It is seen to give off long, 

 multicellular, very thick, brown-coloured threads, which possess 

 numerous fine branches, and are only colourless at their ends. 

 The partition walls between the cells are seen to be placed 

 obliquely. The rhizoids, with which we have here to do, have as 

 their special function the task of fixing the plant in the soil. As 

 organs for absorbing water, they possess, at least in many mosses, 

 only a subordinate importance. 



If a moist sod of Hylocomium triquetrum is placed in a flat 

 dish containing water, the upper parts of the plants soon dry up. 

 This shows that no energetic and adequate conduction of water 

 takes place in the interior of mosses, such as occurs in the higher 

 plants. If, however, we closely observe the clump of Hylocomium 

 lying in water when the summits of the plants are dry, we find 

 that all the stems are moist for a fairly long distance above the 

 surface of the water. Water is therefore raised by the plants to 

 a certain height, and this takes place by capillary attraction. The 

 water rises to that level in the narrow spaces present between the 

 stems and their closely applied leaves ; but obviously those parts of 

 the plants which cannot be reached by this external water supply 

 must dry up. If a vigorous shoot of Hylocomium triquetrum is 

 well dried between blotting-paper, and is then dipped with its 

 base or apex in a solution of an aniline pigment (I used aqueous 

 solution of methyl violet), we readily see that the water rises to 

 some height by capillary attraction. If clumps of Hylocomium 

 or Hypnum, freed from adherent soil, are weighed when in the 

 air-dry condition, immersed in water for say ten minutes, laid on 

 a sloping glass plate, so that the excess of water may drain off, 

 and then again weighed, it is found that they have been able to 

 take up many times their weight of water. This gives us an idea 

 what large quantities of water may be retained by capillarity by 

 the mosses in a forest ; and, in fact, mosses play an important 

 part in many regions in regulating the hygrometric conditions. 

 If we examine transverse sections of the stem of Hylocomium 



