794 A. S. Crafts 



leaf. Under saturated conditions the micro-capillaries must be filled 

 to the surface; under stress, menisci must recede in the capillaries to 

 depths proportional to the extent of the deficit. 



Applied under conditions of saturation regulator molecules in the 

 solution are able to diffuse directly into the living symplast via the 

 water continuum. Applied under conditions of stress the micro-capil- 

 laries are blocked by entrapped bubbles and entry of the regulator 

 is prevented. Inclusion of a liquid surfactant in the formulation en- 

 ables the applied solution to creep around the bubbles and make 

 contact with the water continimm. 



Strugger showed some time ago (14) that dye molecules could 

 move rapidly along the cell walls of mesophyll cells. Some molecules, 

 such as amitrol and MH, may move in this way from the point of 

 application to the periphery of a leaf. Figure 1 shows such movement 



4 Days 8 Doys 



# A ^ * ^ 



*••# ^### 



• m m ^##« 



* # • • 



Mon 



'AA ^ JL 



V hg h4 he V ^2 h4 he V he h4 hg 



Fig. 3. Symplaslic and apoplastic movemcius of coinpouiuls in potato tiibci tissue 

 as shown by autoradiograms after 2, 4, and 8 days. Top, autoradiograms; bottom, 

 nionnlrd tissue. Com|)onn(Is tested were 2,1-0, amitrol (At): maleic hydra/ide (MH). 

 urea, moiunon, ami lAA. Columns represent median vertical slices through one set 

 of tuber blocks (v); horizontal slices 2 mm. in thickness cut 2 mm. (h2), 4 mm. (h4), 

 and f) nun. (hO) from the top of another treated block. 2,1-D, IA.\, amitrol, and 

 MH show symplaslic movement of compounds of increasing mobility. Monurou 

 shows apoplastic movement. Urea was evidently hydrolyzed and the C^O, lost by 

 dilfiision. 



