OEGANS OF REPRODUCTION. 333 



of Milkwort and Spurge, alluded to above, would come under 

 one of the yarieties of arillus, according to their respective 

 origins. Other botanists again, instead of using the two terms 

 strophioles and canmcules as synonymous with each other, apply 

 the former term only when the processes proceed from the hilum, 

 and the latter to those coming from the micropyle. Altogether, 

 there is a great difference of opinion among botanists, as to 

 the application of the terms caruncules and strophioles ; in 

 this country they are more commonly understood in the sense 

 in which we have first defined them. 



2. The Nucleus or Kernel {figs. 728 and 737, n). — The 

 nucleus of the seed corresponds to the same portion of the ovule 

 in a mature condition. In order to understand its structure, we 

 must briefly narrate the changes which the nucleus of the o\nile 

 undergoes after the process of impregnation has been effected. 

 "We have already stated, that at an early period, a quantity of 

 protoplasmic matter of a fluid nature is deposited in the embryo- 

 sac. In this matter nuclei soon make their appearance ; and 

 their formation is succeeded by the development of a num- 

 ber of loose cells (see Cell Development) ; these are first pro- 

 duced upon the walls of the embryo-sac, and their formation 

 extends gradually inwards. A similar development of cells also 

 frequently takes place on the outside of the embryo-sac, and 

 therefore in the nucleus itself, which is in such cases necessarily 

 thickened. These cells, which contain nutritive matters of va- 

 rious kinds, are especially designed for the nourishment of the 

 embryo, which is developed in the sac after the process of ferti- 

 lization. (See Keproduction of Phanerogamia.) 



The embryo, by absorbing the nourishment by which it is sur- 

 rounded, begins to enlarge, and in so doing pi-esses upon the pa- 

 renchymatous cells by which it is enclosed, and thus causes their 

 absorption to a greater or less extent according to the size to which 

 it ultimately attains. In some cases, the embryo continues to 

 develop until it ultimately causes the destruction, not only of the 

 parenchymatous tissue within the embryo-sac, as well as the sac 

 itself, but also of that of the nucleus, in which case it fills the 

 whole interior of the seed, and is coated directly by the integu- 

 ments, which have been just described. At other times, however, 

 the embryo does not develop to any such degree; in which case it 

 is separated from the integuments by a mass of parenchymatous 

 tissue of varying thickness, which may be derived from that of 

 the nucleus itself, or from the nucleus combined with that of the 

 embryo-sac according to the extent to which the embryo has 

 grown ; a tissue will thus remain, forming a solid mass round the 

 embryo, to which the name oiiallmmen has been applied ; but as the 

 nature of this substance is different from that called by chemists 

 vegetable albumen, it is better to designate it as the perispirm. 

 As this albumen or perisperm is sometimes formed as just men- 



