470 SCIENCE PROGRESS 



to the starch grains themselves he does not think they form 

 a typical reserve available for the nourishment of other tissues 

 in the plant, and admits that their true significance " must 

 still be considered an open question." 



As Haberlandt points out in the fourth edition of his Physio- 

 logische Pflauzenanatoinic (1909), one cannot generalise from the 

 starch grains of the Euphorbiaceae. It is not inconceivable 

 that the latex of different families of plants may function in 

 various ways ; that sometimes its possibilities as a food supply, 

 and at other times its protective properties, may occupy the 

 most prominent place. In the case of Broswmm Galadodendron, 

 the cow-tree or milk-tree of Venezuela, large quantities of latex 

 flow out when a notch is made in the stem, and this latex is 

 sufficiently palatable and nutritious to be used by men like 

 ordinary milk. Here at least the latex is rather of the nature 

 of a food than a protection against the animal world. In many 

 other cases, however, it is by no means palatable, and sometimes 

 it is poisonous — eg, the Upas-tree {Antiaris toxicaria) of Java- 

 while its property of coagulating on exposure to air provides 

 a ready means of closing small wounds. 



In the investigations which have been so far dealt with 

 considerable attention has been paid to variations in the 

 amount of starch under diverse conditions of experiment. 

 Many valuable results have been obtained in this way, but 

 it is more important to make similar observations with regard 

 to the sugars present, since the carbohydrates actually travel 

 either in these or other soluble forms. As a rule starch is 

 only deposited when the concentration of these soluble carbo- 

 hydrates exceeds a value varying greatly with different plants. 



The work of Schimper (1885) upon translocation is of par- 

 ticular interest, as he examined in detail the changes in amount 

 undergone both by starch and sugar when leaves were allowed 

 to empty in darkness. After being decolourised in alcohol the 

 leaves were placed in a solution of chloral hydrate in water 

 to which iodine was also added. In this way the tissues were 

 made fairly transparent, and as the agent caused the starch 

 grains to swell, Schimper was able to examine their distribu- 

 tion without cutting the tissues. The sugar distribution was 

 examined by means of Fehling's solution. 



It was found that the disappearance of starch proceeded 



