GROWTH. 



155 



development, the stage of enlargement. This stage is marked 

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

 marked increase in amount of protoplasm present. The in- 

 crease in size, therefore, is mainly due to a great increase in 

 the volume of water, which accumulates in one or more large 

 spaces (C, fig. 117). If the organ in question has an elon- 



FiG 117- — Cells from young and mature fruit of snowberry {Spimfihorfcar^us), seen in 

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

 very minute: By 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 ti ; vacuole single, very large. The volume of C is more 

 than 1500 times one of the cells in A. ^, cell-wall ;/, protoplasm ; k, nucleus-. 

 kkf nucleolus ; s, vacuole. — After Prantl. 



gated form, such as the stem or the root, growth of the cells 

 takes place chiefly in the direction of its long axis. During 

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

 times their former volume. 



EXERCISE XXXVir. 



To measure the rate of growth in length. 



Construct an auxanometer as follows : Take a board 30 cm. square, a 

 common spool, a wheat or oat straw 35 cm. long, and a piece of glass 

 tubing 5 cm. long, which will just allow spool to revolve easily on it. 

 Close one end of the glass tube by holding it in the flame of a Bunsen 

 burner; when hot spread it enough to stop spool from passing over end, 

 by pressing it endwise against a piece of iron. With a fine saw cut a 

 section 5 mm. thick from middle of spool, thus making a wheel. File a 

 groove in edge of this wheel, deep enough to carry a thread. Slip wheel 

 on glass tube and fasten it in board near lower left corner so deep that' 



