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156 A TEXTBOOK OF BOTANY [Cn. IV, 7 



ment is such that the growth of the plant permits 

 a magnifying wheel to turn, and thereby a pen to 

 fall along a cylinder which revolves once an hour, 

 and upon which, accordingly, the pen marks a spiral 

 line crossing any vertical line once an hour. Thus 

 is obtained, night and day without break, an auto- 

 graphic record of the plant's growth, an example of 

 which, precisely traced, is given herewith (Fig. 109). 

 As shown by such an instrument, the growth of 

 any individual part, such, for example, as the 

 flower-stalk of some bulbous plant, exhibits always 

 two striking features. First, as our record well 

 shows, there are many marked fluctuations in the 

 rate. Second, aside from the fluctuations, one can 

 always see that the rate of growth, instead of being 

 uniformly rapid from start to finish, exhibits a slow 

 beginning, a rise up to a culmination where it is 

 most rapid, and then a gradual fall away to cessa- 

 tion as the part approaches maturity. This mode 

 of enlargement, which apparently results inciden- 

 tally from the way the cells expand, is called the 

 GRAND PERIOD. It is apparently characteristic of 

 the growth of all individual parts, viz. of single in- 

 ternodes of stems, of leaves, flowers, fruits, and 

 really (though not apparently) of roots. In struc- 

 tures composed of many unit parts, however, as in 

 a stem with a number of internodes, the grand 

 periods of the parts often overlap, and thus yield 



FIG. 109. The complete record, obtained by the auxograph 

 of Fig. 108, of the growth of a flower stalk of Grape Hyacinth, 

 from its appearance above ground until the completion of blos- 

 soming. It is reduced photographically, from the 8-times mag- 

 nification on the record papers, to the scale of the actual growth. 

 It is also inverted from the record papers and therefore stands 

 in the true position of the growth. Each space on the vertical 

 line marks one hour, and the heavy horizontal lines indicate 

 noon of each day. The lines which run together in the greatly 

 reduced cut are perfectly distinct in the original record. 



