2i6 TRILLIUM. 



complete flower. 5 The so-called flower of Atrichum 

 differs essentially from a true flower in bearing the pri- 

 mary sexual organs (antheridia and archegonia) directly 

 upon the axis of the flower. In true flowers asex- 

 ual spore structures first arise in the shape of pol- 

 len spores and embryo sac, which in turn give rise to 

 the primitive sexual organs as naked cells within these. 

 The first true flowers are met with in Pinus, in which 

 they have no envelopes ; in Avena there is either no 

 perianth, or a very poorly developed one, just as we 

 choose to regard the palet and lodiculesas such or not ; 

 but in Trillium there is a typical perianth. The flower 

 is composed of sets of modified leaves symmetrically 

 clustered at the apex of a short axis. The outermost 

 and lowest whorl (calyx) of leaf-like sepals, a second 

 whorl (corolla) of colored petals, then two whorls 

 of stamens (andrcecium), and a central and uppermost 

 whorl of carpels (gynoecium), all standing upon the 

 broadened apex of a branch (receptacle) may be taken 

 to fairly represent a typical flower. The order given 

 not only expresses the order of occurrence upon the 

 receptacle but also the order of development ; and the 

 type number, three, so characteristic of monocotyle- 

 dens, should be borne in mind (see fig. i). 



The perianth is an arrangement for protection both 

 in bud and blossom, 6 while in the latter stage the cor- 

 olla becomes in addition a device for attraction. 7 



5 For a concise account of the homology and nomenclature of the 

 parts of a flower see Sachs, Text-book, 2nd Eng. ed. , p. 490. 



6 Cf.Kerner, Flowers and their Unbidden Guests. 



7 Cf. Gray, Struct. Bot., p. 215, etseq.: Darwin, Pert, of Orchids ; 

 Effects of Cross and Self-fertilization ; Forms of Flowers etc. 



