MOVEMENTS DUE TO TURGOR AND GROWTH 425 



elastic walls and present a very high osmotic pressure (7-5 atmospheres). 

 Whether the inner layers of the wall exhibit equal osmotic pressure but less 

 extensible membranes, or whether their osmotic pressure is less, does not appear 

 to have been determined ; a difference in the extensibility of the membranes 

 is quite sufficient, however, to account for the result. 



Cydanthera pedata (Hildebrand, 1873) may be compared in all respects 

 with Impatiens so far as its mechanism is concerned, but it differs entirely in 

 its form. The fruit of this plant consists of three carpels, forming a placenta, 

 however, on only one of the sutures, bearing two rows of obhquely-placed 

 seeds. The position of the placenta in the interior may readily be recognized 

 in the asymmetrical fruit (Fig. 130, /), for on this side there is less bulging, 

 and the spines, developed on the other side, are here absent. 



When the fruit is ripe the wall bursts open, from the top downwards, into 

 two longitudinal halves, which curve outwards, so that the exterior of both 

 becomes concave, in consequence of tissue tensions which, however, operate in 

 the reverse way to those in Impatiens. Certain peculiar arrangements in the 

 interior of the fruit facilitate the ejection of the seeds, for the placenta becomes 

 released from that half of the fruit with which it was originally united, but 

 remains firmly attached to the apex of the other curving half, and hence, when 

 the sudden rupture occurs, it is slung backwards, and the seeds are in this way 

 released from their attachment and jerked with considerable force into the air. 



Similar tensions, leading to movements, are found not merely in fruits but 

 in other regions of the plant, and are especially 

 frequent in flowers. The relation of the stamens 

 of many Leguminosae (e.g. Sparthim) to the 

 carina is the only case that need be referred 

 to ; these are suddenly released when the flower 

 is visited by an insect, whereby the pollen is 

 ejected. These phenomena do not appear to 

 have been investigated from the physiological 

 standpoint, so that we need not discuss them 

 further. On the other hand, the ejaculatory 

 movements of the stamens of the Urticaceae i ^ 



have been accurately studied, and a brief pig 130. Fruit of Cydanthera ex- 

 reference may be made to them. Each stamen pMens. i general view. //, longi- 



1 .I n • J • J ii_ J. tudinal section showing manner of 



when the flower opens is curved mwards so that opening ; p, placenta. After hi^de- 

 the anther comes to touch the base of the lila- ^'^^^° ^^^^i'- 

 ment. The concave side of the filament is thus 



in a state of compression and attempts to straighten itself, but cannot 

 do so on account of certain obstacles. At first sight it would appear 

 as if the perianth on the one hand, and ovary on the other, between which 

 the anthers are pinched, were the cause, but, as Askenasy (1879) showed, 

 it is possible to remove a stamen from the flower without any consequent 

 straightening of the filament. The anther is glued to the base of the 

 filament and it is only when this resistance is overcome that the concave side 

 straightens itself, while the anther opens with a sudden jerk, at the same time 

 ejecting the pollen. A touch or a slight heating may accelerate this movement, 

 but it takes place automatically when the osmotic pressure has become sufficiently 

 great. If the filaments be plasmolysed the tension is abolished, and hence we 

 may conclude that osmotic pressure alone is responsible for the movement. The 

 plasmolysed filaments, however, present a certain resistance to attempts to 

 straighten them on account of the fact that the convex sides are more fully 

 grown than the concave sides ; the rapidity of the releasing movement must 

 therefore overcome the resistance offered by the greater length of the convex side. 

 In the discussion of these examples of slinging movements it has been again 



