412 BOTANICAL GAZETTE [JUNE 




ay SRSA, ONES NS aS In all except three plants, in 
Hypocotr! | ootlength|" tescol” which it fell at the middle, the 
hypocotyl ’ 
——— sharpest curve was above the 
a, . me — middle of the hypocotyl (fg. 7). 
ee 9 4. In several of the plants the curve 
: 2. om began immediately at the inser- 
: * : tion of the cotyledons. Two of 
8 | to. 10. 7. the plants of this series were put 
ni : : into water culture vessels, and 
pes : is when the elongation of the hypo- 
13 | 9. 4 5. cotyl was finished, in a south win- 
- ~ oe a dow, the points where the radius of 
Ay.| 3.3mm 72mm | 5.6mm curvature had been least were 20 


and 22™ above the foot of the 
hypocotyl. The curve had disappeared In three plants of another 
experiment the part of the hypocotyl below the sharpest curve 
elongated to 17.5, 18.0, and 19.0", the curve being eliminated. 
With somewhat older seedlings the result is less uniform. 
With twelve plants whose hypocotyl was ca. 10™™ and the root 
ca. 2.0™™" long, placed horizontal for twenty-one hours, the result 
was that the sharpest curve in three hours was in the hypo- 
cotyl, in six hours at the line of separation, and in three hours 
in the root. Before the experiment the plants had been in 
imperfectly saturated air, which shortens the growing region, as 
compared with plants grown in water or saturated air.‘ 
The first attempt at an explanation of the behavior of the 
hypocotyl was by a study of its anatomy. If the transition from 
stem to root character in the internal tissues or their arrange- 
ment occurred higher up than the external line of demarcation, 
there would bea fine prospect of demonstrating the relation of 
3From clinostat experiments I know that both negative geotropism and recti- 
petality are concerned in this straightening. 
4Sacus, J.: Ueber das Wachsthum der Haupt- und Nebenwurzeln. -Gesammelte 
Abhandlungen 807. From Arb. bot. Inst. Wiirzbur re 1. 1874. 
Popovicl, A. P. (Bot. Centralbl. 81 : 33. 1900) ies that several but not all 
factors checking growth shorten the growing region. For influence of insufficient 
water see p. 95 

