■ Growth in Eriogonum nudum 213 



cumstance marks the end of elongation. Within the zone of elongation, 

 the cells are all thin walled with large vacuoles. 



In a very young internode 13 mm. long, the zone of maximum 

 elongation was found to be at the base. In one 60 mm. long, its maximum 

 elongation took place about two-thirds the distance from the base to 

 the apex, the entire zone being 35 to 40 mm. in extent. In an internode 

 199 mm. long, growth took place throughout a zone of 72 mm., 36% of 

 the whole. Towards the end of the grand period of growth, elongation 

 becomes more and more localized nearer and nearer the apex. In the 

 final phase, growth is transverse, bringing the previously tapering 

 shaft into cylindrical form. 



It seems probable that the growing region becomes shortened during 

 the major growth period of the afternoon (as Copeland, 1913, found 

 in Lager stroemia) when the extension of definitive mechanical tissues 

 takes place. My own measurements, however, afforded contributory, 

 but not conclusive evidence of this. 



Like those of the cortex, the cells of the medulla are very thin walled in 

 the growing zone, with thin protoplasmic utricles, and large vacuoles. They 

 contain emulsoids which may be assumed co be pentoses in a very low con- 

 centration. They are dehydrated by alcohol and are rehydrated by water. 



The behaviours of various internodes indicate that their dimensions 

 have considerable relation to their growth rates. The more slender 

 the part the relatively greater the evaporating surface, and the more 

 suddenly the interior is affected by changes in the environment. This 

 seems to account for the irregular growth during the day of the part 

 furnishing the data of August 22nd — Sept. 3. The short-period fluctua- 

 tions for this part are displayed in the table beyond. 



Stomata. — It was found difficult to study the stomata and my 

 results were m.ore or less discordant. The in situ method (Lloyd, '13) 

 could not be used on account of the size and shape of the internodes; 

 and the alcohol fixation of stripped epidermis (Lloyd, '08) could be 

 used only on plants other than the one under observation. 



In the growing region of the long internode the stomata are very 

 immature and are capable of only a very minor amount of movement. 

 The cuticle is at this time but slightly developed, and we may infer that, 

 though the transpiration rates may be low, cuticular transpiration takes 

 a large share in it. It is a question whether the movements of stomata 

 at a distance from the growing region have any close relation with the 

 water balance of the growing part because of the rapid development of 

 dense mechanical structures and of helavy cutinization amounting to a 

 waxy coating, while the leaves have a very dense felt of trichomes on 

 the lower, stomatal surface. 



