TRANSLOCATION OF CARBOHYDRATES 469 



experiment of this kind whether the starch has been used up 

 in nourishing the surrounding tissues or has been employed 

 in the laticiferous tubes themselves. Treub, however, did not 

 consider the latter contingency as at all probable. In addition 

 the exact significance to be attached to the disappearance of 

 starch from particular portions of a non-septate tube is not 

 altogether clear. 



The starch grains in the latex of some Euphorbias have a 

 remarkable power of persisting long after darkening has caused 

 all traces of starch in the parenchymatous tissues to disappear. 

 For instance, in 1885 Schimper, whose results were subse- 

 quently confirmed by Kniep, found that after being in darkness 

 during twelve days the starch grains in the latex of Euphorbia 

 Peplus showed no diminution in size, though they appeared to 

 be rather less numerous. In repeating and extending these 

 experiments Kniep kept one plant of Euphorbia Lathyris in 

 darkness during twenty-two days, and even at the end of 

 that period found " no difference in the starch content of the 

 latex." 



Such a persistence of starch grains also occurs among most 

 plants in the guard-cells of stomata and in the starch sheath. 

 To account for it either the plastids associated with the forma- 

 tion of the persistent grains must be supposed to differ some- 

 what from those producing the starch in the assimilating cells 

 or else the other cell contents must be different in the several 

 cases referred to. In this connection it is extremely interesting 

 to note Kniep's observation that corrosion of the grains only 

 occurs to a very slight extent and only after a long time — a fact 

 which rather suggests some difference in the production of 

 enzymes effecting hydrolysis of the starch. 



Diastase itself does not appear to have been demonstrated 

 as yet in the latex of Euphorbias; indeed Kniep states that 

 the appearance of the starch grains in such latex is never like 

 that of grains artificially exposed to the action of this enzyme. 

 On the other hand, malic acid was found to produce very much 

 the same "melted off" appearance as is actually shown by the 

 starch grains under consideration, and it is well known that 

 calcium malate is present in the tubes. 



Kniep agrees entirely with Schimper that " the laticiferous 

 tubes of the Euphorbiaceae are not concerned to any marked 

 extent with the conduction of carbohydrates." With regard 



