THE DISPERSION OF SPECIES BY MEANS OF FRUITS AND SEEDS. 833 



that this supply is not lost prematurely by evaporation. As a matter of fact, such 

 detached offshoots, e.g. those of Sempervivum, Sedum, Kleinia, or Mamillaria, 

 are not only provided with a special aqueous tissue, but also with a cuticle which 

 is very effective in preventing excessive transpiration. All offshoots, when liberated 

 from their place of origin, are also provided with the necessary reserves, i.e. con- 

 structive materials, so that immediately after settling, they can send out absorbent 

 roots and green leaves of their own initiative, obtain a firm footing in their new 

 locality, and extract nourishment from it. When the offshoots are distributed by 

 water-currents, they require neither an aqueous tissue nor protection against drying 

 up, and it may be due to this fact that detached offshoots are relatively more fre- 

 quent in aquatic than in land plants and lithophytes. 



THE DISPEESION OF SPECIES BY MEANS OP FEUITS AND SEEDS. 



On the heights of the Kahlenberg, at Vienna, at the edge of the wood, grows 

 an under-shrub which bears the name of Borycnium herbaceum. It is one of the 

 Papilionacese, and develops spherical one-seeded fruits, which ripen in October. 

 I once collected from this plant several twigs laden with fruit, for the purpose of a 

 comparative investigation on which I was engaged, and brought them home and 

 laid them on my writing-table. Next day as I sat reading near the table, one of 

 the seeds of the JDorycnivmi was suddenly jerked with great violence into my 

 face. Shortly afterwards I saw a second, third, fourth, and ultimately about fifty 

 seeds let fly from the small clusters of fruit, and each time I heard a peeuKar 

 sound which accompanied the bursting open of the fruits and ejection of the seeds. 

 The rays of sunshine from the window had evidently heated and dried the fruits, 

 and occasioned this surprising phenomenon. The incident reminded me of the 

 following passage in Goethe's Travels in Italy: — "I had brought home several 

 seed-capsules of Acanthus m,ollis, and put them away in an open box, when one 

 night I heard a crackling noise, and immediately afterwards a sound like the 

 impact of small bodies against the walls and ceiling. I could not understand it at 

 first, but found afterwards that my pods had burst and scattered their seeds all 

 over the place. The dryness of the room ha-d caused the fruits to ripen in a few 

 days to the requisite degree of elasticity." 



The fruits of Dorycnium and Acanthus may be taken as types of a large 

 group designated by the name of Sling-fruits. It is found that when these fruits 

 are ripe, the tissue around the seeds becomes highly tense. The first result of the 

 tension is that the tissue is rent at particular spots, and this rupture is followed 

 by a sudden contraction of the segments, which double back and roll up, at the 

 same time expelling the seeds resting upon them. Sometimes the roUed parts of the 

 fruits, and, more rarely, the entire fruits themselves, are jerked off simultaneously 

 with the seeds. There is the greatest variety in this respect, but all the con- 

 trivances for expelling seeds resemble one another in the fact that through their 

 agency the seeds reach places beyond the range of the mother-plants. 



VOL. II. 



103 



