1968 



A TEXTBOOK OF THEORETICAL BOTANY 



m 



in marshes. The inflorescence is a cymose umbel and the flowers are 

 generally trimerous, occasionally dimerous. Generally there is a perianth 

 of two whorls, except in Butomus (Fig. 1894). There are from nine to an 

 indefinite number of stamens and from six to an indefinite number of 

 carpels. These are apocarpous with an indefinite number of anatropous 

 ovules scattered over the inner surface of the ovaries. This last point is 

 of particular interest for it is similar to the condition found in the Nym- 

 phaeaceae. It has been used as evidence to suggest a common ancestor for 

 both families and as an argument for the equal antiquity of the Dicotyledons 

 and Monocotyledons. Hutchinson points out the close similarity between 

 Butomus and Cabomba, the latter also having trimerous flowers and being 

 aquatic in habit. He points out that the only fundamental difference 

 between the two is the paired cotyledons in Cabomba. Hutchinson considers 



that too much importance should not be 

 attached to the number of cotyledons 

 among primitive Angiosperms, for he 

 points out that some members of the 

 Ranunculaceae often possess only one 

 cotyledon. He further suggests that his 

 newly constituted Amaryllidaceae may 



0\ v^^^/ have their origin in the Butomaceae. 



I ^^^i Tht best-known member of the 



(a Mil/ B family is Butomus umbellatus, the Flower- 



ing Rush, which is common in Britain. 



The Naiadaceae are a small family 

 of submerged aquatic plants rooting in 

 the bottom of ponds containing fresh or 

 brackish water. The slender stems are 

 much branched and the leaves are short 

 and narrow, arising in pairs. The margin 

 of the leaf is spiny and this spine, which 

 may arise either from a single cell or 

 from a group of cells, is considered a 

 specific character. The plants (Fig. 1895) 

 may be monoecious or dioecious and the 

 flowers arise from an outgrowth in the 

 axil of a lower leaf. This lateral out- 

 growth bifurcates, one half forming the 

 flower and the other an axillary branch 

 at the base of which the flower finally 

 lies. In the male flower there is only a 

 single anther which may contain one to 

 a perianth and a spathe, which arise as 

 outgrowths below the anther, and the perianth ends above it in four 

 close-fitting lips while the spathe is drawn out above into a cylindrical 

 neck. In the female flower the apex of the floral axis bears a single ovary 



Fig. 1895. — Naias minor. A, Female 

 flower. B, Male flower. N. flexilis. 

 C, Male flower with elongated 

 pedicel. A'^. marina. D. Female 

 flower. {After Rendle.) 



four loculi. It is enveloped in 



