378 HOW CROPS GROW. 



from the stumps of potato, tobacco, and sun-flower 

 plants. He found that successive portions, collected 

 separately, exhibited a decreasing concentration. In 

 sunflower sap, gathered in five successive portions, the 

 liter contained the following quantities (grams) of solid 

 matter : 



1. 2. 3. 4. 5. 



Volatile substance,... 1.45 0.60 0.30 0.25 0.21 



Ash, 1.58 1.56 1.18 0.70 0.60 



Total, 3.03 2.1G 1.48 0.95 0.81 



The water which streams from a wound dissolves and 

 carries forward with it matters that, in the uninjured 

 plant,, would probably suffer a much less rapid and ex- 

 tensive translocation. From the stump of a potato-stalk 

 would issue, by the mere mechanical effect of the flow of 

 water, substances generated in the leaves, whose proper 

 movement in the uninjured plant would be downwards 

 into the tubers. 



Different Kinds of Sap. It is necessary at this 

 point in our discussion to give prominence to the fact 

 that there are different kinds of sap in the plant. As 

 we have seen (p. 289), the cross section of the plant pre- 

 sents two kinds of tissue, the cellular and vascular. 

 These carry different juices, as is shown by their chemi- 

 cal reactions. In the cell-tissues exist chiefly the non- 

 nitrogenous principles, sugar, starch, oil, etc. The 

 liquid in these cells, as Sachs has shown, commonly con- 

 tains also organic acids and acid-salts, and hence gives a 

 red color to blue litmus. In the vascular tissue albumin- 

 oids preponderate, and the sap of the ducts commonly 

 has an alkaline reaction towards test papers. These dif- 

 ferent kinds of sap are not, however, always strictly con- 

 fined to either tissue. In the root-tips and buds of 

 many plants (maize, squash, onion), the young (new- 

 formed) cell-tissue is alkaline from the preponderance of 



