THE BLEEDING OF INJURED PLANTS 255 



are immersed in water so that only the cut end projects, the latter begins 

 after a time to bleed. The aid of the leaves is, however, unnecessary, for 

 branches denuded of them may also exude water if the corky layers 

 are removed, or if the wood is partially exposed so that water can be 

 absorbed, while at the same time its escape through the cut ends of the 

 immersed twigs is prevented by a covering of varnish, or by means of 

 india-rubber caps. In this case the active cells which absorb water and 

 force it into the vessels evidently form part of the living stem. Such cells 

 are also present in leaves, as the positive results of a few experiments show. 

 Hence, in certain cases, the leaves may aid in producing the exudation- 

 pressure exhibited when experiments are carried out in this manner. 

 A similar action has also been observed in the stems of herbaceous plants, 

 in the peduncles of flowers, or inflorescences, in rhizomes, bulbs, &c. 

 A visible example is afforded when pieces of young grass stems are buried 

 in wet sand, for drops of water soon exude from the projecting upper end 

 of the grass haulm. 



The roots undoubtedly excite the most active exudation of water, but 

 that is simply because they are the best absorptive organs the plant possesses. 

 Nevertheless, the root-stock does not always bleed more actively than 

 do portions of the stem, and, indeed, in several plants an active exudation 

 of water has been observed only from isolated pieces of the stem. No 

 decisive conclusion can, however, be drawn from experiments of this kind 

 as to what may be the precise part played by any given organ in the 

 intact plant. It is, however, at once evident that the different parts of 

 a plant co-operate to very unequal extents in producing the phenomenon in 

 question, while the parts played by the individual cells of an organ differ 

 very widely from one another. 



The exudation of water cannot always be produced in the same manner, 

 or by the same means. The power of bleeding differs frequently at different 

 periods of development, and in certain cases is induced only by the action 

 of special external conditions (Sect. 44). The contradictory opinions often 

 expressed concerning the bleeding power of a particular plant are due to this 

 fact, as well as to individual peculiarities, while for the most part the obser- 

 vations relate only to the roots, or stumps of the stem *. Most of the higher 

 plants are apparently capable of an active exudation of water either always 

 or only at certain times. Nevertheless, the same genus may contain bleeding 

 as well as non-bleeding species, and hence too much importance must not 

 be attached to the fact that most of the Coniferae experimented with can 

 bleed but little or not at all. It is, moreover, not surprising that mosses 

 also can bleed, for here the same cell activities come into play as are 



1 For details see Wieler, 1. c., p. 13. 



