INTRODUCTION TO BOTANY. Xvii 



§ 13. The Ocnle. 



117. The ovule is a minute body borne by the placenta (Ho) and 

 destined, after fertilization, to become the seed. At first it is merely a 

 cellular excrescence, but as it enlarg-es it acquires a definite foi-m and 

 structm-e, and when fully lirowTi consists of a central mass or uuchus; en- 

 closed in one or two bag-like coats, the oiiter called primine, the inner 

 seciaidine. The nucleus is the essential part ; in it the tmhryo is formed 

 after fertilization. The coats afterwards become the integuments of the 

 seed. 



118. The ehalazo is that point at which the base of the nucleus is con- 

 fluent with the coats of the ovule, and is generally discoloured in the seed. 

 The /«rfr;/?r» is the common aperture of the coats, opposite the apex of the 

 enclosed nucleus, and through which the pollen is acbnitted in fertiliza- 

 tion : in the seed it is called the microi^yk. 



119. Ovules are said to be, 



orthotropous or strai[/ht (or atropous^^ when the chalaza or organic 

 base coincides with the apparent base of the ovule, and the 

 foramen is situated at the opposite extremity, the ovule having 

 a rectilinear axis : as in the Nettle, Dock, Fig, etc. 



cainpylotrop(jus or incurred, when, the base remaining the same, the 

 axis is curved dowTi and the foramen directed towards the base ; 

 as in the CaryophyUefe and many leguminous plants. 



(OHitrnpoiifi or imerted, when the chalaza, in an ovule with rec- 

 tilinear axis, is removed to the point most distant from the 

 hilmn, and the foramen brought close to the hilum. It is like 

 an orthotropous ovule reversed on its cord ; the cord adhering 

 to one side of the oviile and becoming more or less incorporated 

 with its coats. Such an adhering cord, appearing either like a 

 line or a ridge, is called the raphe : it connects the hilum mth 

 the chalaza. Anati'opous ovules are much the commonest ; 

 good examples of distinctly marked raphe and chalaza may be 

 found in the Orange and the Pansy. 



amphifropous or huJf-inrerted, when the raphe extends but half the 

 length of the ovule, and the chalaza and foramen, at opposite 

 ends, are about equidistant from the hilimi : as in the Mallow 

 tribe, the Primi'ose, etc. 



§ 14. The Receptacle and relative attachment of the Floral Whorls. 



120. The Receptacle, or iorm, is the extremity of the pedvmcle (above 

 the caljrx) upon which the corolla, stamens, and ovary are inserted. It is 

 sometimes little more than a mere point, but it is often more or less 

 lengthened, thickened, or otherwise enlarged. [The tenn receptacle is also 

 extended to the summit of a branch or inflorescence, on w^hich the flowers 

 of a head are inserted, as in the Compositoi.'] 



121. A disk, or disc, is a circular enlargement of the receptacle, usually 

 cup-shaped, flat, or cushion-shaped {pulrinate), and often of a waxy or 

 fleshy appearance. It is situated either inmiediately at the base of' the 

 ovary within the stamens, or between the petals and stamens, or bearing 

 the petals or stamens or both at its edge, or quite at the extrf^uiity of the 

 receptacle, with the ovai-ies arranged in a ring round it or under it. 



122. The disk may be entire, toothed, lobed, or divided into a number of 

 parts, usually as many or twice as many as the stamens or carpels. When 

 the paris of a divided disk arc separate and short, they are often called 

 glands. 



123. Nectaries are either the disk, or small deformed petals, or abortive 



