4 A. B. Rendle. — Najadaceae. 



Floral Structure (Blütenverhältnisse), in the fertile shoots (Fig. \ A, D) a tf or Q 

 flower occupies the place of the lowest (scale-)leaf and its bud. The flower originates, as 

 Magnus showed, by the dichotomy of an axillary branch. A protuberance arises at the 

 growing-point in the axil of the lower leaf of each pair before the appearance of the upper 

 leaf. This protuberance becomes divided by a vertical furrow into a slightly larger lower, 

 and a slightly smaller upper rudiment. The former develops into a flower, the latter into 

 the branch at the base of which the flower is apparently borne in the mature condition. 

 The floral axis is therefore homologous to an axillary branch. Sporogenous tissue develops 

 in the apex of the floral rudiment which becomes in the female the nucellus of the ovule, in 

 the male the anther. 



In the female an annular wall grows up round the developing ovule ; its margin becomes 

 2 — 3-lobed according to the number of the stigmas, and when fully developed forms a 

 closed Chamber containing the ovule. The time and mode of origin of the outer envelope 

 in N. indica and its allies have not been observed. The integuments of the ovule arise, 

 first the inner, then the outer, after the ovary-wall has become partly developed. 



In the male a symmetrical ring arises round the base of the anther, and subsequently 

 a second appears inside the outer and remains always closely adherent to the anther. There 

 is^ no sign of a midrib or of the division of either of these sac-like outgrowths into leaves. 



This floral development is of great interest. (l) The flower arises by the dichotomy 

 of an axillary branch. (2) The sporogenous tissue is produced in the tip of the floral axis. 

 (3) The homology of the envelopes is difficult to explain in the ordinary terms of the parts 

 of a flower. 



In course of development the cup-like wall surrounding the ovule and the outer 

 envelope of the anther are homologous, while the inner envelope which remains closely 

 adherent to the anther corresponds with the integuments of the ovule. Magnus regards the 

 carpel-like structure in the female flower as the homologue of the cup-like envelope round 

 the group of carpels in the allied genus Zannichellia. The latter also arises as an annular 

 outgrowth of the floral axis , but surrounds more than one rudiment each of which ulti- 

 mately develops into an ovule surrounded by a stigma-bearing ovary-wall. Magnus suggests 

 that the arrangement in Najas may have arisen from such a type by the suppression of all 

 the ovules but one, and all the ovaries, leaving a naked ovule surrounded by a cup-shaped 

 envelope (or perianth) which then developed stigmatic appendages. Najas, on this view 

 becomes a gymnosperm, the female flowers of which have one, more rarely two, sac-like 

 perianth envelopes corresponding with the two in the male. 



This view has not been generally accepted. Campbell has shown that in Zannichellia 

 we have a group of monocarpellary flowers , that is , an inflorescence. He also remarks on 

 the primitive character of the flowers in Najas and it is in the primitive simplicity of the 

 flower that we must seek the clue to the arrangement. We have in both male and female 

 an axial structure containing sporogenous tissue which develops respectively into structures 

 obviously comparable with a normal anther and nucellus, the latter becoming surrounded by 

 integuments forming a normal ovule. The ovule is surrounded by a cup-like outgrowth, 

 which recalls the development of the ovary in Polygonum or Rumex (see Payer, Traite 

 d'Organogenie tt. 64, 65) and which has the appearance and form of an ovary. The inner 

 envelope in the male flower I regard as a perianth. It is a lateral outgrowth of the floral 

 axis below the androecium, which it protects, and has therefore the characters of a perianth 

 which has arisen rather late in the history of the flower-development. The outer sac which 

 characterizes the male, and is occasionally present in the female I have called a spathe 

 (Fig. \ C, F), remembering, however, that it is simply an outgrowth of the axis which 

 ends in a flower, below that flower. It is comparable with the spathe so characteristic of 

 submerged monocotyledonous water-plants, which may have, moreover, a very similar 

 appearance (e. g. Lagarosiphon, Hydrilla etc.). It will then correspond, as Magnus sug- 

 gested, with the cup-like envelope in Zannichellia, which on Campbell' s Interpretation 

 becomes a spathe surrounding an inflorescence, as in the Aroids. 



