THE ANGIOSPERMAE 1231 



dary development in the ontogeny of the flower. Considered functionally, 

 its value lies in placing the stigma in the position where it will be most 

 effective in pollination and its existence and the amount of its development 

 seem to depend on this need. Thus, we generally find that there is little, if 

 any, stylar growth in open, actinomorphic flowers with simple pollination 

 mechanisms and that its development is greatest in sympetalous and 

 especially in zygomorphic flowers. Its function may, indeed, be taken over 

 by other parts, as for example by the elongated ovary itself or by the 

 development of an axial gynophore, which may raise the stigma to an appro- 

 priate level without the intervention of a style. Alternatively, the stigma 

 itself can become elongated so that it replaces the style, though it is a matter 

 of words only whether one describes such elongated structures as style-less 

 stigmas or as styles which are stigmatiferous throughout their length. They 

 are sometimes distinguished as stylodia and are to be found in their highest 

 development in wind-pollinated flowers. 



Let us consider first the case of the single, free carpel. In many, 

 perhaps in the majority, the suture runs up to the carpel apex and both the 

 margins are either wholly or partly stigmatiferous. The stigmas may be 

 united into a single structure or remain divided into two by the carpel 

 suture, depending upon the degree of union obtaining between the carpel 

 margins. The stigma therefore, even when it appears unitary, is of double 

 origin. Robert Brown believed this to be true of all stigmas, but although 

 widespread, the condition is not universal. In the alternative case the carpel 

 suture does not extend to the apex, the carpel primordium terminating in a 

 hood, and it is this structure, more or less extended into a solid column, or a 

 tube if the loculus is involved in the extension, which bears the stigma 

 terminally. As the hood belongs to the dorsum of the carpel, such stigmas 

 may be called dorsal, as opposed to the ventral stigmas which originate from 

 the carpel margins and in which the dorsum may play no part, as shown by 

 the absence of the dorsal vascular bundle. The dorsal stigma is, moreover, 

 a single structure from the beginning. We may say that in the second case a 

 style has been formed, and none in the first case. 



Not that this is the only way in which a dorsal stigma may be formed. 

 In HeUeborus, for example, we can see transitions between ventral and 

 dorsal conditions. Here the ventral suture runs right up to the carpel apex. 

 The dorsum is elongated into a style and the suture forms a groove along it, 

 while the stigmatic surface in different species may be produced either on 

 the edges of the groove (the ventral condition), or may extend on to the 

 dorsal region and finally become localized on the dorsally produced style, 

 where it usually forms a single structure. In Drimys (sect. Tasmannia) 

 (Fig. 1 190), where ventral stigmas are primitive, the carpel margins are 

 fully stigmatic in some species, while in others the stigma is confined to a 

 small crest near the apex. In the related genus Zygogymim the dorsum 

 remains short and the ventral portion overgrows it, carrying the stigmatic 

 crest over to the dorsal side, though it is not of dorsal origin. The dorsal 

 stigma may therefore be either primary or secondary, according to the 

 G 



