PROTOPLASM AND ITS PROPERTIES 



183 



194, Nature and Occurrence of Irritability in Plants. 1 - 

 Mention has already been made of the fact that certain 

 parts of plants respond to suitable stimuli that is exciting 



n 



FIG. 12fi. Protoplasm in Ovule and Fruit of Snowberry (Symphoricarpun 



racemosus). 

 A, cells from ovule, x 340 ; B, cells from an ovule further developed, x 340 ; (', />, 



cells from pulp of fruit, x no ; n, nucleus ; p, protoplasm ; s, cell-sap. 

 In the young and rapidly growing cells, A and J5, the cell-sap is not present, or 



present only in small quantities, while in the older cells, C and D, it occupies 



a large portion of the interior of the cell. 



causes. Geotropic movements (Sect. 70) are due to 

 the response of roots or shoots to gravitation. These 



1 See Strasburger, Noll, Schenk, and Schimper's Text-Book of Botany, 

 Pp. 160-162 and 269-274. 



