118 



CHARLES S. RIDGWAY 



callose were found attached to the walls in epidermal cells which 

 produced no root-hairs. In these instances the pads occurred on 

 any except the inner wall (fig. 7). 



The shape of the lumen necessarily varied according to the 

 nature of the thickening. In some cases of uniform deposit of 

 callose the cavity of the hair was entirely obliterated. This 

 condition was found also when only a plug occurred in the hair or 

 when the callose was found at either of its extremities. In others 

 the lumen was closed for a shot distance, then appeared further 

 on only to be closed again toward the extremity of the hair (fig. 

 1). These open places in many cases contained protoplasm and 

 in others were empty. In plugged hairs the protoplasm is found 

 on both sides of the plug in some and on one side only in others 

 (figs. 4 and 6). In this last case a resemblance is seen to the 

 "cellulose" plugs found in the pollen tubes of members of the 

 Rubiaceae and in many representatives of other families.^ 



Though Haberlandt* indicates that the lumen of the root-hair 

 is conveniently continuous for the purpose of rapid transfer of 

 absorbed substance, nevertheless several cases of septate root- 

 hairs, both callosed and thin walled, have been found among those 

 observed during the progress of this work (figs. 3 and 10). Though 

 the partitions represented in figure 3 appear to be mere bars of 

 callose extending across the lumen and not true septae, cases of 

 callosed, septate hairs were found. The irregular outline of the 

 cross walls shown in figure 10 were believd to be due to the begin- 

 ning of callose formation, despite the failure to get a definite 

 reaction in this particular case. 



Microchemically, the substance responsible for the thickening 

 of the hairs seemed to conform sufficiently to the following tests, 

 according to Zimmerman,^ Haberlandt® and Strasburger and 

 Hillhouse^ to prove its identity with the callose of sieve plates, 

 etc. : 



'Lloyd, F. E., p:mbryology of the Rubiaceae. Mem. Torr. Bot. Club, 8: 98, 

 xxxx. 



* Haberlandt, G. Physiologische Pflanzenanatomie, 1904, p. 195. 

 ' Zimmerman, A., loc. cit. 

 ^ Haberlandt, G., loc. cil. 



' Strasburger, E and Hillhouse, W., Handbook of Practical Botany, 1911. 



