I CARBOHYDRATES, CHITIN AND CUTIN 281 



called cell plate in the phragmoplast of the staminal hairs of Trades- 

 cantia first becomes visible as droplets exhibiting a Brownian move- 

 ment. They do not, he says, move along the spindle filaments, as is 

 assumed by others, but are formed, just where they are, by dissoci- 

 ation from the dense plasm (Becker, 1935). The drops adhere laterally 

 and form a grained isotropic membrane which, however, does not at 

 first touch the side walls and shows a pectic reaction (coloration with 

 ruthenium red). Plasmolysis reveals its independence. From the 

 moment when this system has grown completely through the phrag- 

 moplast and has reached the wall of the mother cell, this diaphragm 

 becomes visible between crossed nicols. Apparently the phragmoplast, 

 split into two halves, immediately generates cellulose on its surface 

 where it is in contact with the new membrane. It seems to me im- 

 probable that a cellulose frame would develop from the droplets 

 described by Becker. It is also difficult to understand how proto- 

 pectin could be formed from liquid drops. I therefore suspect that 

 the drops are water of hydration liberated when high-polymeric chain 

 molecules are built up in the cell plate from sugars of low molecular 

 weight. The fact that the microvacuoles are dyed vitally with basic 

 dyes (neutral red) does not invalidate this view, since they may quite 

 conceivably contain water-soluble components, though they can 

 scarcely harbour insoluble high-polymeric material such as proto- 

 pectin or cellulose. These wall substances must be formed submicro- 

 scopically in the phragmoplast and do not become visible until a 

 microscopic system of protopectin has been built up, against which 

 cellulose mixed up with protopectin is then immediately deposited on 

 both sides. Hence the original middle lamella and both primary walls 

 are already present in this very young state, but presumably all three 

 membranes increase in thickness before surface growth begins. 



Cell elongation. The submicroscopic morphology of elongating cell 

 walls is familiar. All meristematic cells capable of elongation are of 

 tubular texture, as has been demonstrated in the case of Avena cole- 

 optiles (SoDiNG, 1934; Bonner, 1935), of the staminal filaments 

 (ScHOCH-BoDMER, 1936; Frey-Wyssling, 1936c), thc rapidly growing 

 sporogonous stem of the moss Pellia (Overbeck, 1934; Van Iterson, 

 1935), to mention only a few. Likewise cotton hairs (Wergin, 1937), 

 bast fibres and all derivatives of cambium (Meeuse, 1938, i 941) possess 

 extremely thin, scarcely visible primary walls of tubular texture. The 



