192 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



that the same is true of the majority of other growing cells. The electron- 

 micrographs of the wall of Phycomyces recently published by Frey- 

 Wyssling(73) reveals a structure in the primary wall a good deal more 

 complex than had been supposed, though his conclusions are supported 

 neither by the electron-micrographs of Roelofsen nor of our own (62). It 

 is certain that the present proposals are based on far too simple prem- 

 ises, but nevertheless we may have some confidence that they are 

 expressed in terms of the correct and relevant variables in the wall. 



a > 



.♦ 



^' 



_L 



2 3 4 5 



Time (hours) 

 •••••, Rotation ; x — x — , elongation 



Fig. 65. The rotation and elongation of a sporangiophore of Phycomyces after a 

 temporary cessation of growth caused by immersion in a 0002% aqueous solution 

 of dodecyl trimethylammonium bromide. Note that the rotation changes sign at the 



minimum on the rotation curve. 



It is very clear, however, even with Phycomyces that this is not the 

 whole story, and it seems possible that these reactions which can be 

 explained in terms of wall extension are in a sense the aftermath of the 

 more fundamental stages in growth. Thus, if a growing sporangiophore 

 is immersed for a short time in a solution of a suitable dye (62) 

 then the whole wall of the growth zone becomes deeply stained. 

 If the cell is then allowed to grow, the growth zone becomes progressively 

 less stained as the young wall present during staining is left behind, 

 becoming part of the adult wall by deposition of secondary lamellae, 

 and is replaced by new wall developed from above. When the 

 sporangiophore has elongated by about 2 mm. (the length of the growth 



