TRANSLOCATION OF CARBOHYDRATES 461 



into " sugar " and " starch " leaves. Among the former come 

 most of the Monocotyledons. According to Czapek the sieve- 

 tubes do not serve to store assimilates but simply to convey 

 them to the storage tissues in v^^hich they are then deposited. 

 He himself was able to show that the assimilates are not 

 conducted horizontally to any great extent through the paren- 

 chyma of the cortex, etc. 



In March he took twigs of willows and of poplars, 30 cm. 

 long and i — 2 cm. in diameter, and removed the tissues 

 outside the cambium so as to leave near the lower end a 



17 u 



Fig. 17. — Diagram to show formation of callus (black) in ringed twig. 



Fig. 18. — Diagram to illustrate Czapek's experiments with petioles. The shading 

 here indicates starch. 



connecting strip consisting of three portions, an upper and 

 a lower vertical, and a middle part longer than either running 

 horizontally (fig. 17). The twigs were kept in a warm, 

 saturated atmosphere and in diffuse light. After twenty-five 

 days under these conditions it was found that in some cases 

 callus had developed below the upper edges of the wound 

 (a) and along the sides of the upper vertical connecting strip 

 (b). Immediately beneath this upper vertical strip the develop- 

 ment of callus was more vigorous, and in one or two cases 

 rootlets also had appeared (c). Along the horizontal limb, 

 however, the formation of callus was restricted to within a 



