GROWTH 



197 



This may be determined by covering the organs while young with 

 evenly spaced indelible marks, and noting the alterations in spacing 

 as growth proceeds. 



EXPERIMENT, (a) Select a plant with rapidly growing leaves, 

 and mark some of the younger of these into equal areas of known 

 size, say 2 -mm. squares. Place under favorable 

 conditions for growth, and, when grown, compare 

 the spread of the marks with the original spacing. 



(b) Using either the same plant, or another 

 with rapidly growing, slender, nearly naked stem, 

 mark this while young by evenly spaced lines, 

 say 2 mm. apart; place under conditions favor- 

 able for growth, and later note the spread of the 

 marks. 



(c) Germinate some strong seeds (Horse Beans, 

 Corn, Peas) in sphagnum; when the roots are 

 about 2 cm. long, lay one flat on the damp moss 

 and mark it from the tip backwards with evenly 

 spaced marks, say 2 mm. apart. Arrange with 

 a clean thistle-tube so that the seed is packed 

 with wet moss in the bulb, and the root is in the 

 tube (Fig. 52), which is slightly inclined from the 

 vertical to bring the marks upward, so they will 

 not rub off. (Or an equivalent from glass tub- 

 ing or from two glass plates may be arranged.) 

 Place under conditions favorable for growth, and 

 note the spread of the marks. 



SPACE-MARKERS. Various simple arrangements 

 may be improvised, such as laying the part on a moist 

 surface close beside a ruler and making the marks 

 with a fine brush, a pen, or a stretched thread dipped FIG. 52. ARRANGE- 

 in waterproof India ink. Or the leaves may be MENT FOR STUDY OF 

 punched by pins set through a flat cork in squares 2 

 m'm. apart But very much better for efficiency and 

 convenience are rubber-stamp markers, of which 

 two forms are to be supplied among my normal ap- 

 paratus. For roots and stems the marker is a wheel 

 (Fig. 53) with its rim of cross lines 2 mm. apart; it turns freely on a han- 

 dle and may be rolled along the part, rnarking it perfectly in a moment. 

 For leaves the marker is a disc ruled in 2-mm. squares which may be pressed 

 by spring or scissors-like handles (Fig. 54) against the leaf, which is held on 

 another disc provided with a slot for the petiole and made soft by a layer 

 of felt. 



The stamps are inked on a sheet of glass, on which waterproof India ink 

 has been thinly and freshly spread. Care must be taken in marking the 

 roots that these are not long exposed to the dry air of the room. 



GROWTH OF ROOTS; 

 Xf 



The bulb is packed with 

 sphagnum moss. 



