280 THE FLOWER. 



at all a seam, as the Greek word denotes. Its origin, and the 

 whole structure of such ovules will be apprehended by comparing 

 various stages of its growth. 



526. Ap ovule of any kind at the beginning is an 

 excrescence or outgrowth of the placenta, or of some 

 part of the leaf-surface if there is no developed 

 placenta. This incipient ovule is the nucleus (518), 

 or the nucleus surmounting a rudimentary funiculus. 

 The nucleus is soft cellular tissue only, from first to 

 last. The achlamydeous ovule (519) undergoes no 

 further development except in size or shape. Indeed 

 sometimes (as in Balanophorese) this bare nucleus 

 is reduced to a few cells of parenchyma. 



527. In ordinary ovules a new growth early begins around 

 the base of the nucleus, or is sometimes coetaneous with it, at 

 first as a ring (or part of a ring) , soon as a cup, at length as 

 an enclosing sac or covering, open at the top ; this is the inner 

 coat of the ovule when there are two. The outer coat begins and 

 goes on in the same way, and at length grows over and encloses 

 the inner coat as that did the nucleus. (Fig. 590-595.) When- 

 ever there is a third and more exterior coat it is formed during 

 the growth of the fertilized ovule into the seed, to which there- 

 fore it belongs, and in which it takes the name of arillus. (597.) 

 At the time of fertilization the apex of the nucleus, or a pro- 

 longation of it, usually projects beyond the orifice and there 

 receives the descending pollen-tube. Some fibro- vascular tissue, 

 especially spiral ducts, may be found in the funiculus and cha- 

 laza, sometimes extending into the coats. 



528. The development of the orthotropous or atropous (un- 

 turned) ovule proceeds symmetrically, without distortion, the 



parts keeping their primitive direction. In the campy lotropous, 

 the whole of one side of the ovule greatly outgrows the other. 



FIG. 689. Magnified view of a vertical section of a carpel of Magnolia Umbrella, 

 about a month before anthesis, showing one of the two nascent ovules, at this time 

 only nucleus. 



FIG. 590-597. Further development of the ovule of Magnolia Umbrella, showing the 

 formation of the coats and the anatropy. 590. Ovule a week older than in 589. 591. 

 Same a week or two later. 592. Same a few days later. 693. Same from a nearly full- 

 grown flower-bud. 594. Sameattimeof anthesis. 595. Vertical section of the last through 

 the middle of the rhaphe. 596. Cross-section of the same. (See Jour. Linn. Soc. ii. 108.) 



