THE CONDUCTION OF WATER. I 51 



thus 1-4-1-9 per cent, of sugar has been found in the birch, in Acer plata- 

 noides 1-2-3-2 per cent., in Acer saccharinum 3-6 per cent., in Agave americana 

 as much as 8-8 per cent. (SCHRODER, 1869). 



The amount of sap excreted from day to day varies very considerably ; 

 sometimes it amounts only to a few drops, at other times it reaches several 

 litres. It may not be without interest to present here, in tabular form, some 

 of the maxima which have been observed (compare PFEFFER, Phys. I, p. 240 ; 



WlELER, 1893 ; MOLISCH, 1898). 



Plant. Observer. Amount per day in litres. 



Vitis aestivalis . . . . (CLARK) ...... 0-227 



Vitis vinifera .... (CANSTEIN) ..... i-o 



.; 8* 



Birch ...... (WlELER) . . . . V 5-1 



Ostrya ...... (CLARK) . . * '','*. . 5-6 



Birch ...... (CLARK) . . . > .6-8 



Agave americana .... (HUMBOLDT) * , . 7.5 



Phoenix dactylifera . . . (SEMLER). ...';. 8-0-10-0 (a) 



Musanga ..... (LECOMTE) . . . -' * . 17-0(6) 



Caryota urens . . . . (SEMLER). . . *'.''. 50-0 (a) 



(a) Whether SEMLER'S results are to be depended upon must remain an open question. 

 MOLISCH did not obtain such large amounts. 



(b} Calculated on the results obtained during 10 hours. 



The maximum outflow is not generally attained at once upon making the 

 incision ; usually there is at first a gradual increase in the amount excreted, 

 followed later by decrease ; we are unable, however, to attribute these varia- 

 tions to any definite external causes. BARANETSKY (1873) has shown this rise 

 and fall very clearly in numerous tables which he has compiled, and MOLISCK 

 (1898) also has given us the following numbers as applicable to Arenga sacchari- 

 fera, where the amounts excreted in ccm. during fourteen days are indicated : 



i 2 3 4 56 7 8 9 10 ii 12 13 14 

 Day . . . 440 500 1500 1400 1300 2050 1640 

 Night. . . 675 1080 2175 2 9 335 J 35o 



Total in 24 hours 1115 1580 3675 4300 4650 3400 - 1440 3600 2500 1140 700 175 o 



From an examination of the table it will be seen that, taking into considera- 

 tion the amount of sap excreted in the twenty- four hours, there is a gradual 

 increase up to a maximum which is reached on the fifth day, followed by a de- 

 crease until the fourteenth day, when excretion ceases. It is also worthy of note 

 that the decrease is by no means gradual and regular, but that a second maxi- 

 mum occurs on the ninth day. It is possible that the second rise may have 

 been induced by external conditions, but in any case irregularities such as these 

 exhibit themselves repeatedly and even more strikingly in experiments carried 

 out in the laboratory under the most equable conditions, so that we are justified 

 in assuming that the plant works irregularly owing to internal causes. There 

 is yet another fact which the table teaches us, and that is, that the amount 

 excreted by day is considerably less than that excreted by night. 



Great variations also exhibit themselves in the duration of the outflow 

 after the infliction of the wound. In palms the excretion often continues for 

 two or three months ; in Arenga it lasts for several years, and in Agave ameri- 

 cana, whose sap (as in the case of palms) is used for the preparation of an 

 alcoholic drink, the bleeding may continue, according to HUMBOLDT, for four or 

 five months. The outflow continues for a shorter period in our indigenous trees 

 (one month), and is most limited in small plants, where it may last for a few days 

 only. Generally speaking, however, the lower limits of the duration of bleeding 

 have not as yet been accurately determined. As a matter of fact, changes, 

 which bring about an occlusion of the lumina of the vessels and a consequent 



E 2 



