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A TEXTBOOK OF THEORETICAL BOTANY 



phyllaceae, Silene and Viscaria for example, have narrow membranous 

 appendages, on each side of the petal-claw, which can only be regarded as 

 stipules. They are, moreover, quite distinct from the paired invaginations 

 which form the paracorolla in Lychnis, Melandriiim and some other members 



of the family. 



In Hypecoiim (Fumariaceae) the stipules of the two internal petals are 

 retracted to a position external to the petal and are so much larger and more 

 conspicuous than the petal itself that the latter might be mistaken for an 

 outgrowth of the stipules, did not the floral diagram show the true position. 



The outer petals, on the other hand, have 

 only two stipular wings of moderate size. 

 The flowers of the Sapindaceae pro- 

 vide a very interesting series of develop- 

 ments in petal stipules, beginning with two 

 inturned marginal lobes, which in some 

 genera become united adaxially, forming, 

 with the petal, a cup. Finally, in Serjania 

 (Fig. 1136), the fused stipules separate 

 from the petal and stand up independ- 

 ently, forming an inner ring, like a second 

 corolla or paracorolla, of small, bifid seg- 

 ments. 



The awns on the floral parts of grasses 

 are for the most part the terminal por- 

 tions of the glumes, paleae, etc., on which 

 they occur, the blade-like portion of these 

 structures, which is frequently bifid at the 

 apex, being probably stipular in nature. 

 When the apex is not bifid it forms a 

 crest across the adaxial side of the awn, 

 analogous to the ligular crest on vegetative grass leaves, a structure which 

 itself may also be either bifid or united. 



The subject of fusions between corolla parts during the evolution of the 

 flower is one we have already mentioned when considering the floral 

 phyllotaxis. The most conspicuous category is that of tangential, i.e., 

 marginal, fusion between members of the same corolla whorl, in cyclic 

 flowers, to produce a floral tube. This condition, called sympetaly, occurs 

 sporadically in some families of the Archichlamydeae, namely Rham- 

 naceae, Crassulaceae and Papilionaceae, but is a uniform characteristic of 

 all the families which form the group of the Metachlamydeae; e.g., Primu- 

 laceae, Scrophulariaceae, Compositae, etc. Among these floral types there 

 is an almost endless variety of forms, the description of which, by them- 

 selves, without relation to their functions in pollination, would lead no- 

 where. The appropriate place for their treatment is in the consideration of 

 the families of Angiosperms (see Chapters XXVIII to XXX and Chapter 

 XXIV on Pollination). We should remark here, however, that striking 



Fig. 1 1 36. — Serjiiniii, petals of 

 various species showing the 

 development of petal stipules 

 from two basal lobes into a 

 united structure opposed to 

 the petal. (After Velenovsky.) 



