88 HYP9COTYLS, EPICOTYLS, ETC., CHAP II. 



Dr epicotyl, being thus saved from abrasion and 

 pressure whilst breaking through the ground. But 

 we think that some importance may be attributed to 

 the increased force gained by the hypocotyl, epicotyl, 

 or other organ by being at first arched ; for both legs of 

 the arch increase in length, and both have points of 

 resistance as long as the tip remains enclosed within 

 the seed-coats; and thus the crown of the arch is 

 pushed up through the earth with twice as much force 

 as that which a straight hypocotyl, &c., could exert. 

 As soon, however, as the upper end has freed itself, 

 all the work has to be done by the basal leg. In 

 the case of the epicotyl of the common bean, the 

 basal leg (the apex having freed itself from the seed- 

 coats) grew upwards with a force sufficient to lift a 

 thin plate of zinc, loaded with 12 ounces. Two more 

 ounces were added, and the 14 ounces were lifted up 

 to a very little height, and then the epicotyl yielded 

 and bent to one side. 



With respect to the primary cause of the arching 

 process, we long thought in the case of many seedlings 

 that this might be attributed to the manner in which 

 the hypocotyl or epicotyl was packed and curved 

 within the seed-coats ; and that the arched shape thus 

 acquired was merely retained until the parts in question 

 reached the surface of the ground. But it is doubtful 

 whether this is the whole of the truth in any case. 

 For instance, with the common bean, the epicotyl or 

 plumule is bowed into an arch whilst breaking through 

 the seed-coats as shown in Fig. 59 (p. 92). The 

 plumule first protrudes as a solid knob (e in A), which 

 after twenty-four hours' growth is seen (e in B) to be 

 the crown of an arch. Nevertheless, with several 

 beans which germinated in damp air, and had other- 

 wise been treated in an unnatural manner, little 



