334 Exogenous Seeds and Fern Spores. 



is composed of a cell called a nucleus, within "which is the 

 germinal sac, containing the germinal vesicle. In the amniotic 

 fluid, attached to the germ sac, is the suspensor. If the 

 mature germ fill merely its sac, the rest of the nucleus is filled 

 with vegetable albumen (see Cainpanulacege), or the germ may 

 fill both its sac and nucleus (see Compositas). 



Now this gerni sac is formed by a depression at the apex 

 of the nucleus, the edges meeting ; but at the point where 

 they meet is the spot where the future root will make its first 

 appearance. Whatever coverings may grow over the seed, 

 they avoid this spot, which, in time, becomes a little hole, and 

 called the foramen or micropyle, marking the organic apex 

 of the nucleus. The organic base is marked by the chalaza, 

 where are seen fibro-vascular bundles passing forwards from 

 the funis or umbilical cord to the nucleus. 



The hilum marks where" the funis joins the seed to the 

 placenta. 



The nucleus may simply be an erect ovule, when the base 

 will correspond with the hilum, or it may make a procession 

 till the apex comes down to the hilum, or may retain any 

 intermediate position. Moreover, the nutrient matter may 

 make a bend on itself, in which case the seed will be said to 

 be camptotropal or curved like a horse-shoe. 



Around the nucleus may be coverings, called intine and 

 extine, being developed from its base. Moreover, it may 

 have another covering, as in the mace or spindle-tree, called 

 an arillus, developed from the chalaza or from around the 

 foramen . 



A perfect seed, therefore, consists of a nucleus, a germ, 

 and a germ sac, which latter contains the embryo of an 

 ascending and descending axis, together with nutrient matter, 

 having a foramen of exit and certain coverings. 



When a seed begins to grow, having imbibed water, the 

 radix pushes forward through the foramen, and if the coats 

 of the seed be thin, they rupture irregularly from the pres- 

 sure, so that, at firsl Bight, it would seem as though there 

 were no foramen. WTiile the radix pushes its way out, the 

 autrient matter within has been undergoing changes: starch 

 becomes, through diastase, dextrine and grape sugar. Mean- 

 while the germinal spot lias arranged itself, and the plumule 

 or ascending axis can be I raced ; fche nutrient matter supplying 



benance bo the several parts, as in wheat or barley; or else 

 it forms itself into primary Leaves, as In the bean or mustard, 



not having ei gh matter in itself entirely to nourish tho 



plumule. Therefore these leaves elaborate matter taken from 

 the ground by i\\c radix, and so indirectly support it. 



If tho spores of ferns bo carefully examined, there will 



