28 OUTER INTEGUMENT. [BOOK i. 



namely, upon the seed becoming ripe the external integument 

 is gradually absorbed, until nothing but a thin membrane is 

 left, usually described as epidermis testa, or in the Spurge- 

 worts (Euphorbiacese) it has been given as aril ; and, on the 

 other hand, the actual modified epidermis testae has also been 

 described as the aril, for instance, in the Oxalids. 



The cellular tissue of the integuments of the seed is very 

 often reticulated. In most Bignoniads, and many other 

 plants, the epidermis is in this state, and in Casuarina there 

 is a layer of spiral vessels below the epidermis, very thin and 

 delicate, and extremely minute. In Swietenia febrifuga there 

 is, below the epidermis, a thick layer of large spiral cells, 

 which have little cohesion with each other, and which form a 

 multitude of rather large fusiform sacs lying confusedly (?) ; 

 this is the most complete case of spiral cells in seeds with 

 which I am acquainted, and it is accompanied by the presence 

 of a bundle of numerous slender spiral vessels in the raphe. 



The outer integument is either membranous, coriaceous, 

 crustaceous, bony, spongy, fleshy, or woody; its surface is 

 either smooth, polished, rough, or winged, and sometimes is 

 furnished with hairs, as in the cotton and other plants, 

 which, when long, and collected about either extremity, form 

 what is called the coma (sometimes also, but improperly, the 

 pappus) . It consists of cellular tissue disposed in rows, with 

 or without bundles of vessels intermixed : in colour it is 

 usually of a brown or similar hue : it is readily separated 

 from the inner integument. In Maurandya Barclay ana it is 

 formed of reticulated cellular tissue; in Collomia linearis, 

 some Salvias and others, it is caused by elastic spirally twisted 

 fibres enveloped in mucus, and springing outwards when the 

 mucus is dissolved. In the genus Crinum it is of a very 

 fleshy succulent character, and has been mistaken for albu- 

 men, from which it is readily known by its vascularity. Ac- 

 cording to Brown, a peculiarly anomalous kind of partition, 

 which is found lying loose within the fruit of Banksia and 

 Dryandra, without any adhesion either to the pericarp or the 

 seed, is a state of the outer integument ; it is said that in 

 those genera the inner membrane (secundine) of the ovule is, 

 before fertilisation, entirely exposed, the primine being reduced 



