58 PART I. MORPHOLOGY. [ 17 



with the sporophylls, or with the sporangiferous axis, of a flower, 

 to which they form an investment termed the perianth. A perianth 

 is present only in Phanerogams, and is confined almost exclusively 

 to the Angiosperms: the Grnetacese are the only Gymnosperms 

 in which it is represented. The leaves may be arranged in a single 

 whorl, or in two or more : they may be all alike, either green and 

 inconspicuous, or of other bright colours and conspicuous ; but 

 most frequently the leaves of the outer whorl (sepals constituting 

 the calyx] are small and green in colour, being especially protec- 

 tive in function, whilst those of the inner whorl (petals consti- 

 tuting the corolla) are large and brightly coloured, being especially 

 attractive in function. (For further details, see The Flower, 

 Part IV.) 



17. General Morphology of the Sexual Reproductive 

 Organs. The general morphology of the sexual reproductive 

 organs agree in many respects with that of the asexual reproduc- 

 tive organs. 



In the great majority of plants the sexual reproductive organs 

 give rise to sexual reproductive cells, termed gametes (p. 2) ; hence 

 the organs may be generally termed gamctangia. In some cases 

 the formation of gametangia is limited to a certain portion of the 

 body of the gametophyte which differs more or less from the 

 vegetative portions of the shoot and may be distinguished as 

 a gameiophore. When a part of the body is differentiated as 

 a shoot, the gametophore is part (or the whole) of the shoot. 



(a) The Gametes. A gamete is a sexual reproductive cell a 

 reproductive cell, that is, which is incapable by itself of giving 

 rise to a new organism ; in this respect it differs from a spore. A 

 spore is, however, formed from the fusion of two gametes of 

 different sexes : that is, by a sexual process (see p. 50). 



In those of the lower Algae and Fungi in which sexual spore- 

 formation takes place, the gametes produced by the organism are 

 all externally similar ; hence these plants are termed isogamous ; 

 the sexual process, which consists here in the fusion of two similar 

 gametes, is termed conjugation ; and the spore formed by conjuga- 

 tion is termed a zygospore. 



In all the higher plants, hence termed heterogamous, the gametes 

 are not all alike ; but there are two kinds, the male and the female. 

 The male and female gametes may be generally distinguished by 

 their difference in size, the male being the smaller, and by the 

 greater activity of the male gamete in connection with the sexual 



