ORGANS OF BEPRODUCTION. 



323 



enclose the nucleus except at its apex {fig. 720). The inner 

 coat is at first seen to project beyond the outer, but the latter 

 ultimately reaches and en- 

 closes it. The inner coat is Fig. 720. Fig. 721. 

 usually termed the secun- 

 dine, s, and the outer \hepri- 

 mine, p. Schleiden and some 

 other botanists call the se- 

 cundine, the integumentum 

 prinnan intermim, and the 

 primine, the integumentum 

 secundum externum', which 

 on the whole are the best 

 terms, as they indicate, not Fig. 720. Ovule of the "Walnut (J^iglans 



1 ii. J ^ J 1 regia). w. Nucleus, s. Coat covering the nu- 



only the order Ot develop- cleus except at the foramen, end. Fig. 



ment of the coats, but also ^21. Ovule ofa species of Po?i/(/o»«tm. /.End 

 ,v . T ,. ... o of ovule attached to the placenta, p. Pri- 



their relative position, bome mine. *•. Secundine. ex. Exostome. e?id.Eu- 

 Other botanists again, fol- dostome. n. Nucleus. 

 lowing the order of development of the coats, term the inner 

 coat the 'primine, and the outer the seciindine, thus reversing the 

 order of names as above mentioned. The orifice left at the apex 

 of the nucleus, as in the former instance where only one coat is 

 present, is called the foramen or mkropyle. The openings in 

 the two coats commonly correspond to each other, but it is some- 

 times found convenient to distinguish them by distinct names; 

 thus, that of the outer is called the e^vostome {fig. 721, ex), that 

 of the inner, endostome, end. The nucleus and its coat or coats 

 are intimately connected at one point by a cellulo-vaseular cord 

 or layer, called the chalaza {figs. 722 and 723, ch) ; at the other 

 parts of the ovule they are more or less distinct. This chalaza is 

 the point where the vessels pass from the placenta, or when the 

 ovule is stalked from tlie funiculus into the ovule for the purpose 

 of affording nourishment to it ; it is generally indicated by being 

 coloured, and of a denser texture than the tissue by which it is 

 surrounded. The chalaza is by some considered as the organic 

 base of the ovule, and the micropyle as the organic apex ; but it 

 is better to speak of the hilum as the organic base of the ovule, 

 and the chalaza as the base of the nucleus. Through the mi- 

 cropyle or organic apex of the ovule, the influence of the pollen 

 is conveyed to the embryo-sac, as will be hereafter fully described. 



The formation and structure of the ovules as described above 

 refer only to those of Angiospermous plants ; those of Grymno- 

 spermous plants present some very striking differences, which 

 will be best described afterwards under the head of Eeproduction 

 of the Gymnospermia. 



Kelation of the Hilttm, Chalaza, and Microptle to each 

 OTHER. — When an ovule is first developed, the point of union of 

 t2 



