SLING- FRUITS. 



835 



of 



The Dorsteniacea, behave in a manner no less remarkable. As in the 

 F: g s so also ln these plants, numbers of small flowers are seated upon an ened 

 receptacle whl ch remains fleshy and succulent after the sma.1 one-seeded fruits have 

 developed from the flower, The lower portion of each fruit h M thick walls, and J. 

 embedded m the receptacle like a hair-follicle in the human skin, whilst the delicate- 



Fig. 459. -Sling-fruits. 



i Orobus vernus. 2 and Geranium palustre. * Viola elatior. Cardamine impatient. 

 ? and s Acanthus mollis. and 1 Ricinus communis. 



Impatient Nolitangcrt. 



coated portion projects above the receptacle in the form of a papilla. When the 

 seed is quite ripe the turgidity of the outer cellular layer of the thick wall of the 

 fruit increases, the thin- walled top is torn, the thick walls suddenly close, and the 

 seed hitherto enveloped by them is violently ejected. 



A special case of the expulsion of seeds as from a sling is also found in Oxali- 

 daceae, of which the common Wood-sorrel (Oxalis Acetosetta, see figs. 458 8 - 4> 6 ) may 

 be taken as an example. In this case it is the seed -coat that possesses a special 

 tumescent tissue adapted to the expulsion of the seeds. One of the deeper layers 

 of the seed-coat is composed of tense cells and is itself in a highly strained condition, 



