XX INTRODUCTION. 



attached, sometimes a mere point or line on the inner surface, often more or less thick- 

 ened or raised. Placentation is therefore tlie indication of the part of the ovary to 

 which the ovules are attached. 



132. Placentas are 



axile, when the ovules are attached to the axis or centre, that is, in plurUocular 

 ovaries, when they are attached to the inner angle of each cell ; in vmhocular simple 

 ovaries, which have almost always an excentrical style or stigma, wlien the ovules are 

 attached to the side of the ovary nearest to the style ; in unilocular comi^ound ovaries, 

 when the ovules are attached to a central protuberance, column, or axis rising vip fiom 

 the base of the cavity. If this column does not reach the top of the cavity, the pla- 

 centa is said to he free and central. 



parietal, when the ovules are attached to the inner surface of the cavity of a one- 

 ceUed compound ovary. Parietal placentas are usually slightly thickened or raised 

 hues, sometimes broad surfaces nearly covering the inner surface of the cavity, some- 

 times projecting far into the cavity, and constituting partial dissepiments, or even 

 meeting in the centre, but without cohering there. In the latter case the distinction 

 between the one-celled and the several celled ovary sometimes almost disappears. 



133. Each Ovule (121), wlien fully formed, usually consists of a central mass or 

 nucleus enclosed in tw^o bag-like coats, the outer one called primine, the inner one 

 secundine. The cJialaza is the point of the ovule at which the base of the nucleus is 

 confluent with the coats. The foramen is a minute aperture in the coats over the 

 apex of the nucleus. 



134. Ovules are 



orthotropous or straight, when the chalaza coincides with the base (36) of the 

 ovule, and the foramen is at the opposite extremity, the axis of the ovule being straight. 



campylotropous or incurved, when the chalaza stiU. coinciding with the base of 

 the ovule, the axis of the ovxxle is curved, bringing the foramen down more or less to- 

 wards that base. 



anatropous or inverted, when the chalaza is at the apex of the OTule, and the 

 foramen next to its base, the axis remaining straight. In this, one of the most frequent 

 forms of the ovule, the chalaza is connected with the base by a cord, called the rliaphe, 

 adhering to one side of the ovule, and becoming more or less incorporated with its 

 coats, as the ovule enlarges into a seed. 



ampMtropous or half-inverted, when the ovule being as it were attached laterally, 

 the chalaza and foramen at opposite ends of its straight or curved axis are about equally 

 distant from the base or point of attachment. 



§ 12. The Receptacle and Relative Attachment of the Floral JVhorls. 



135. The Heceptacle or torxis is the extremity of the peduncle (above the calyx), 

 upon wliich the coroUa, stamens, and ovary are inserted. It is sometimes little more 

 than a mere point or minute hemisphere, but it is often also more or less elongated, 

 thickened, or otherwise enlarged. It must not be confounded with the receptacle of 

 inflorescence (74). 



136. A Disk, or disc, is a circular enlargement of the.receptacle, usually in the form 

 of a cup (cu2mlar), of a flat disk or quoit, or of a cushion (pulvinate). It is either 

 immediately at the base of the ovary within the stamens, or between the petals and 

 stamens, or bears the petals or stamens or both on its margin, or is quite at the ex- 

 tremity of the receptacle, with the ovaries arranged in a ring round it or under it. 



137. The disk may be entire, or toothed or lohed, or divided into a number of parts, 

 usually equal to or twice that of the stamens or carpels. When the parts of the disk 

 are quite separate and sliort, they are often called glands. 



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

 or appendages at the base of petals or stamens, or any smaU bodies within the flower 

 which do not look like petals, stamens, or ovaries. They were formerly supposed to 

 supply bees with their honey, and the term is frequently to be met with in the older 

 Floras, but is now deservedly going out of use. 



139. When the disk bears the petals and stamens, it is frequently adherent to, and 



