PHYSIOLOGY 



321 



the assistance of wind, raiu, and animals aided by the existence of 

 cracks and crevices in the ground. The fixation of the seed in the 

 soil, which is often of importance for the emergence of the seedling 

 from the testa, is assisted by structural peculiarities of the surface 

 such as furrows, ridges, bristles, and 

 hairs ; the latter may be able to expand 

 hygroscopically. 



Tin- fruits of the Geraniaceae (Erodiurii, 

 Fig. 222) and Gramineae (Stipu, Aveim utmlix. 

 and species of ^Ir-isfida) are enabled, by means 

 of movements due to hygroscopic torsion as- 

 sisted by the presence of stiff backwardly- 

 directed bristles to bury themselves in tin- 

 ground. In the cast- of Ti-lj'nl In-lit, subter- 

 runcuni and v//v/'7//.s- hypogtua&e same result 

 is accomplished by the geotropic growth of the 

 fruit-stalks, while the seed-capsules of Linariu 

 cymbaJaria are deposited in the crevices of 

 walls and cliffs by the negative heliotropic 

 movements of the fruit-stalks. Nuts, acorns, 

 and seeds buried by squirrels or other animals 

 in the ground and forgotten, or for any reason 

 not made use of, often germinate. The seed- 

 lings of Mangrove trees, llhr.nplwru, Bruguiera, 

 and Kandclia (Fig. 250), exhibit a most 

 peculiar manner of growth to ensure their 

 lodgment in the ground. The seed germinates 

 in the fruit before it is detached from the tree. 

 When the radicle, has attained a considerable 

 length, the young seedling, separating either 

 from the cotyledons or from the fruit-stalk, 

 falls to the earth, boring like an arrow into 

 the mud, in which it sticks erect and is thus 

 enabled to commence its growth without del.-i\. 

 In some species of the Mimosaceous genus 

 Inya naked embryos are also liberated from tin- 

 fruits or seeds. 



Many seeds and fruits acquire a more or 

 less voluminous MUCILAGINOUS SHEATH, which 

 serves a double purpose. Quince seeds, Flax 

 seeds, seeds of the Plantain, of Crucifers, tin- 

 fruits of S" //-in Imi-inimiiii, seed of Cuphea and 

 CobfK'u (in the mucilage cells of which delicate 



thickening bands are rolled up), afford the best-known examples of such slimy 

 envelopes, which, in addition to fixing the seed to the ground, serve to absorb 

 water by holding it in their substance or drawing it in hygroscopically (cf. 

 Mistletoe berries). Fruit -walls, by their spongy nature, may also serve a> 

 water-carriers (ripe fruits of Tropaeolum, Pvti-i'ii' m xfi'tnosum, Medieuyo terebellmn). 



In the soil the seed swells quickly or more slowly and then at 



Y 



I'n.. -'.Mi. Kinnlelia llAeedii. The mass- 

 ive root (it the seedling (/) has broken 

 out of the fruit. When the ]>l;mt 

 separates from the fruit the root will 

 become inserted into tin; muddy soil. 

 (After S( HIMPER'S /V,i,,M,Vo,,n</>/ry.) 



