84: OVULE. 



and tropos, form). This is the case in comparjitively few 

 plants. The Polygonums, JSTettles, Walnuts, and a few othei-s, 

 are in this manner, but scarcely ever the Monopetalge. Oftener 

 than otherwise the ovule undergoes changes during its develop- 

 ment, so that the various parts bear very different relations. 

 The most frequent change is where the ovule is completely re- 

 versed ; that is, the apex of the nucleus is in contact with the 

 placenta, and the base of it in the opposite direction. In tliis 

 case the bundle of vessels that we called the funiculus becomes 

 extended between the primine and secundine to the base of the 

 nucleus, and is called a raphe (raphe, a line). (Fig. 137, r.) 



139i The place of attachment of the raphe to the base of 

 the nucleus is called the chalaza. (Fig. 137, ch.) An ovule 

 thus inverted is said to be anatropous {a privative, and 

 tropos, implying the opposite of the former). This is the 

 most common form in the vegetable kingdom. Almost all 

 Monopetalc'e, the greater number of Monocotyledons, and 

 many of the Polypetalae, have anatropous ovules. There is 

 another variety which is quite common in Polypetala?, in which 

 the base of the ovule remains fixed, 

 but by an enlargement of one side ^'^- ^^• 



of the ovule more than the other, it ^ k^5^==^v^^__«, 



is bent or doubled on itself, so as to A--v^^^ ^^ 



bring the foramen in close proxim- (^ ^y/p^^^___^y n 



ity to the funiculus. (Fig. 138.) ( \^^ Ifj 



This form is called the campylotro- \\ //J 



pons {kampulos, curved, and tropos, ^^^^^^ 



form.) LeguminosDc, Solanje, Cru- „^ „„,,,„3 . „^ .ecundine ; h, pr,-. 

 ciferae afford examples of this form. Suiu?;' offmSn/'' ^''"™' ^' 

 Other forms are pointed out by bot- 

 anists, but we have found them of no practical importance. 

 The same letters in the preceding figures point out the same 

 things. 



140. The ovule usually has two distinct coverings, as above 

 described, but this is not universal. Sometimes it has none. 

 The nuclei of some Dipsaceae, Asclepiadre, and Cuscutaceaj are 

 naked. The nuclei of the Compositae, Labiatae, Scrophulan- 

 aceiie, and Campanulaceae, and some others, have but one in- 

 tegument. 



141, Some time before the expansion of the flower, the apex 

 of the nucleus is hollowed out by a greater or less cavity, 



Is this form common? How do the vessels run? What is the bundle 

 called? — 139. What is the chalaza? What is a campylotropous ovule! 

 140. Is the nucleus always covered ? 



