THE BLEEDING OF INJURED PLANTS 253 



partly plasmolytic, and partly active, and it is in many cases still uncertain 

 which of the two processes is at work, or when both are active, which is 

 of the greater importance. Nevertheless, as a general rule, bleeding, as 

 well as the excretion of water from water-pores, &c., is an active secretory 

 process, whereas the excretion of water in nectaries is due to plasmolytic 

 action. In both cases the osmotic powers of living cells are involved, for 

 in producing the plasmolytic excretion of water the living plant creates the 

 necessary conditions, i. e. it produces and excretes the osmotic substances 

 which induce an outward flow of water. 



The exudation of water is simply a special example of the varied 

 processes of excretion and absorption without which living cells could not 

 continue to exist (cf. Sect. 23). Wherever particular parts are endowed 

 with a special secretory activity, we may term them glands, whether we 

 are dealing with a single cell (hairs, &c.), or with organs of complex 

 structure. A distinction can be made between digestive glands, sugar-glands 

 or nectaries, and water-glands, the ' Emissaria' of Moll and the ' Hydathodes' 

 of Haberlandt being simply water-glands 1 . Nectaries may also be regarded 

 as water-glands, if we pay attention only to the fact that they can excrete 

 water, though the actual withdrawal of water is due to the plasmolytic 

 action of the sugar which the cells of the nectary excrete. Water-glands 

 may be further classified in a variety of ways, either according to their 

 shape or morphological nature, or according to the position of the secreting 

 cells or of the exit channels. Burgerstein uses the special term ' Guttation ' 

 when the vvater escapes through water-pores z . 



The phenomenon of bleeding may be dealt with first, for it has been 

 the most deeply studied. An explanation of the causes which induce 

 bleeding will give the key to a comprehension of the active secretion from 

 uninjured organs. 



x. 



SECTION 42. The Bleeding of Injured Plants. 



By bleeding or weeping is meant the exudation of water under pressure 

 from injured regions, such as may take place, for example, when stems, roots, 

 branches, or even leaves are cut across, or when a hole is bored into the 

 trunk of a tree. The phenomenon of bleeding has been known from very 

 ancient times in the cases of the vine and maple. When holes are bored into 

 the stem of the latter in spring-time, large quantities of sap gradually flow 

 out ; if the stems or branches of the vine are cut, water exudes from them and 



1 Moll, Unters. iiber Tropfenausscheidung u. Injection, iSSo (Sep.-abdr. a. Meded. d. Konig. 

 Akad. d. \Yetenschappen 2, Bd. xv) ; Haberlandt, Sitzungsb. d. Wien. Akad., 1894, Bd. cm, 

 Abth. i, p. 494. All organs capable of excreting water can also absorb it when a deficiency exists 

 in the plant, just as the root may be caused to excrete water instead of absorbing it (cf. Sect. 34). 



2 Burgerstein, Material, zu einer Monog. d. Transpiration, 1889, i, p. 5. 



