222 



BOTANY OF THE LIVING PLANT 



to receive the pollen, and to enclose and protect the Ovules. (Fig. 

 1 68, ov.) Under favourable conditions each ovule is able to produce 

 a single new germ, and to develop into a mature Seed. 



The relations of these floral parts to the receptacle are similar to 

 those of the foliage leaves to the stem ; for they arise laterally upon 

 it, and their succession is such that the oldest are the lowest, or outer- 

 most, and the youngest the inner- 

 most, or nearest to the tip. No 

 buds are produced in their axils. 

 As in the foliage shoot the appen- 

 dages may be arranged spirally, or 

 in whorls, but in the flower the 

 latter is the more common. The 

 members of the successive whorls 

 usually alternate with one another. 

 This is convenient for their close 

 packing in the bud. The parts of 

 the flower are as a rule closely 

 aggregated together, while those of 

 the vegetative shoot may be separ- 

 ated by long internodes. But all 

 normal leafy shoots terminate in a 

 bud, and so, at least in the young 

 state, the two are alike in this also. 

 There are thus marked analogies 

 between the foliage shoot and the flower. Both are constructed on the 

 same plan. There is, however, one absolutely distinctive character which 

 separates them. It is the presence in the Flower of the Organs of Propa- 

 gation, called Sporangia. These have no correlative in the vegetative 

 region. They are organs of a separate category altogether. Accord- 

 ingly the Flower may be defined as a simple Shoot which bears Sporangia. 

 In the Flowering Plants the Sporangia areoftwo sorts, viz. Pollen-Sacs 

 and Ovules. In very many cases these are both present in the same 

 flower, which is then called Hermaphrodite. But in others only one 

 or the other is present. When the flower contains stamens bearing 

 pollen-sacs, but no carpels, it is described as Staminate ; when it has 

 carpels bearing ovules, but no stamens, it is called Pistillate. The bio- 

 logical importance of these differences of distribution is great, as they 

 are closely related to the mechanism of intercrossing. 



The two types of sporangia, viz. pollen-sacs and ovules, and the parts that 

 bear them, viz. the stamens and carpels, are often described as organs of sex, and 



FIG. 169. 



(i.) Single male flower of Spurge (Euphor- 

 bia,), consisting of one stamen, with abortive 

 perianth, (ii.) Single female flower, consisting 

 of three carpels, and an abortive perianth, 

 (iii.) ' Single male flower of j^A nthostema 

 (Euphorbiaceae). 



