156 A TEXTBOOK OF BOTANY [Ch. IV, 7 



| merit 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- 



E 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 



E 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. 



