THEAMP:RICAN botanist 109 



^rcw. As more pdwcrful aj:^ciits, sucli as lijj^lit, dampness, 

 obstructions. gravitatii Ml. etc. exert llieir inllueiices llu' plant be- 

 comes susceptible lbeiel<i and in tliis \\a\". new movements 

 were developed, wbicli lia\e become liereditary and necessary 

 for tlie well l)ein«( of tbe plant. 



KS I'l N ASTV MOVEMKNTS 



When the growth is i^reater longitudinally along the upper 

 tlian along the lower side of the i)arl. causing a downward 

 bending, the term es[)inasty is used. The rexerse ot this is 

 expressed by hxponasty. These are in realit)- modifications 

 of circuniiuitalion, but because the\- are so often referred to, 

 the special terms were designated to ex[)ress them. The 

 organ, under the influence (hf epinasty does not move down- 

 ward in a straight line, or upwards under the influence of hy- 

 ])onasty. but (iscillates up and down with some iaieral move- 

 ment. Howe\er. the preponderant nioxenient is up and down. 

 There i> some growth on all sides of the part, but more on 

 tbe u])per in tbe case of epinast\' and more on the lower in 

 that of liy])onasty. There may be an additional growth on 

 one side due to geotropism and on another side due to helio- 

 tropism. thus increasing or decreasing ejMnasty ov hyponasty. 



I )ne of tlie commonest cases of epinastv is that offered 

 bv leaves which are crowded together rotmd tbe l)u<ls at an 

 earl\- age and diverge as tbe plant grows older. It was be- 

 lie\ed that thi> is due to increased growth along the upi)er 

 side of the petiole blade. As the hypocotyl and epicotyls of 

 some plants protrude from the seed coats in an arched form, 

 it is doubtful whether the arching through the ground ought 

 always to be attributed to epinasty; hut wIkmi it happens that 

 they are first straight and afterwards become arched, it is in 

 that cave certainly due thereto. The arch must retain its 



