SPERMATOPHYTES 



131 



phylls. A flower, therefore, may be said to be a strobilus 

 with a perianth. Originally a flower was thought to be 

 essentially a group of sex-organs, and therefore a sexual 

 structure. It is evident that it consists of members (peri- 

 anth and sporophylls) borne by a sporophyte, and there- 

 fore it cannot be a sexual structure. It is impossible to 

 apply the term strobilus and flower strictly among Angio- 

 sperms, for some flowers have no perianth because they have 

 never had one, and 

 therefore are strobili; 

 and others have no 

 perianth because they 

 have lost it, and there- 

 fore are flowers by de- 

 scent. Among Angio- 

 sperms, therefore, it is 

 convenient to speak of 

 all sporophyll-bearing -^ j / 



structures as flowers. 



81. The perianth. / FlG 101 _ Flower of peon y : &, sepals (forming J 



It is evident that the \ the cal y x ); c > P etals (forming the corolla); 



calyx and corolla^ together constiiuig the perir 



perianth IS the distin- j "SS&Z a, starnenTf O, carpels (oT^istils). After 

 . , . i r , STRASBURGER. 



guishing mark of a \ 



flower; in fact, it is just the mark that people in general 

 use in recognizing a flower. One of the features of Angio- 

 sperms is the endless variation in the structure of the 

 perianth, so that the different kinds of flowers become the 

 most valuable means of classifying Angiosperms. 



The term perianth is a collective one, to include all the 

 members ; but it is used chiefly in cases where the members 

 are all approximately alike, as in the lilies and their allies. 



\ In most Angiosperms, however, the perianth is differentiated 

 into two sets, calyx and corolla (Fig. 101). The calyx, 

 whose individual members are called sepals, is the outer 



\set and usually green in color; while the corolla, whose 



