SEED. 



109 



distinguishable testa and endopleure; often, when ripe, all the coats merge into 

 one, or one splits up into several layers, and the seed presents three or four 

 coats. The origins of these envelopes will be described under the development of 

 the ovule. 



Arils are accessory organs, which mostly develop after fertilization, and cover 

 the seed more or less completely, without adhering to the testa ; some are expansions 

 of the funicle, and are specially designated as aril (arillus) (Nymphcea, Passiftora, 

 Opuntia, Willow, Yew) ; others arise from the dilatation of the edges of the micro - 

 pyle, and are called by some authors arillodes or false arils (arillodes). 



In the White Water Lily (fig. 610) a swelling (A, A), rising from the funicle (F), 



gradually spreads over and caps the 

 ovule, and ends by closely enveloping 

 the seed, without adhering to it, leaving 

 scarcely a trace of an opening over 

 the chalaza (Ch.). In Passion-flowers 



M. 



Ck J 



610. White Nymphffia. 



Vertical section of the young 



Seed (mag.). 



6H. Yew. 



611. Willow. Ripe fruit, sunk in 

 Seed (mag.). its fleshy aril. 



615. 616. 617. 618. 



European Spindle-tree, showing the successive 



developments of the arillode. 



an annular swelling, with a free membranous torn margin, forms at the shortened 

 end of the funicle, round the hilum ; this gradually expands, and ends by en- 

 closing the seed in a loose fleshy bag, with a large opening towards the chalaza. 

 In Willows (fig. 611), the very short thick funicle expands into an erect pencil 

 of hairs, which envelops the seed. In Cactus Opuntia, two concave boat-shaped 

 expansions spring laterally from the funicle, into which the ovule is pushed, 

 and within which it is developed ; this accessory envelope thickens, hardens, and 

 forms a sort of stone, covered with pulp. In the Yew, the female flower (fig. 612) 

 consists of a single ovule, which is at first protected only by the scales of the bud 

 from which it issued, and after fertilization disengages itself from these, when it is 

 completely naked, with a gaping micropyle at its summit. Soon (fig. 613), between 

 the ovule and the scales at its base, a small cup is developed, which gradually swells, 

 becomes red and succulent, and ends by almost entirely covering the seed (fig. 614) ; 

 this cup is nothing but an enormous development of the funicle, which thus furnishes 

 an envelope to the fruit, which had not'even the protecting scale of the Pines and 

 Firs (tig. 379). In the Spindle-tree (figs. 615, 616, 617, 618), the successive stages 

 of development of the arillode (a) are easily followed (1, 2, 3, 4) ; it does not spring 

 from the funicle (/), but from the micropyle, the edges of which dilate by degrees so 

 as to form around the seed a succulent, loose, folded bag, open towards the chalaza. 



