GROWTH. 



179 



they pass gradually from the embryonal stage into a second 

 phase of development, the stage of elongation. This stage is 

 marked by the rapid increase of the cells in size and a much 

 less marked increase in the mass of protoplasm present. In 

 order to maintain the turgor of the cells, there is a great in- 

 crease in the volume of water, which accumulates in one or 



FIG. 181. Cells from young and mature fruit of snowberry (Sy>///>horicar/>us), seen in 

 section. A, three young cells, very small, walls thin, nuclei relatively large, vacuoles 

 very minute; , two, somewhat older, larger, walls thicker, nuclei smaller, vacuoles 

 several. A and B magnified 300 diam. C, a single cell, mature, magnified 100 

 diam., one third as much as A and B ; vacuole single, very large. The volume of 

 C is more than 1500 times one of the cells in A . h, cell-wall ; /, protoplasm ; k, nu- 

 cleus; kk, nucleolus; s, vacuole. After Prantl. 



more large vacuoles (C, fig. 181). If the organ in question 

 has an elongated form, such as the stem or the root, growth of 

 the cells takes place chiefly in the direction of its long axis, 

 although an increase also occurs in the transverse directions. 

 During this phase the cells may attain a hundred or even a 

 thousand times their former volume. Growth in length can 



