76 THE STAMENS. [CHAP. 



leaves of the stem and the stamens or carpels, especially 

 the latter. But the acceptance and thorough apprecia- 

 tion of this view you will find furnishes an invaluable key 

 to the comprehension of all the various modifications 

 which the stamens and pistil undergo ; and it is especially 

 with reference to these that we shall at present concern 

 ourselves. 



19. THE STAMENS. The more important of the cha- 

 racters afforded by the stamens, due to varying conditions 

 as to cohesion, adhesion, and suppression, have been 

 already, directly or indirectly, referred to. Each stamen 

 may be the homologue of a single leaf, as is usual when 

 the stamens equal in number the parts of the corolla or 

 calyx, or each stamen may answer to a lobe of a divided 

 or compound leaf, as is clearly the case when stamens are 

 polyadelphous, and may probably be so in respect of their 

 origin in many diplostemonous and polyandrous flowers 

 in which they are free, as well as in some, like the Mallow, 

 in which they are indefinite and monadelphous. 



The anther may be sessile or, as is usually the case, 

 borne upon a filament which stands in the same relation 

 to the anther as the petiole to the blade of a foliage-leaf. 

 Anthers vary in form usually from linear or oblong to 

 ovate or cordiform. The pollen in each anther is con- 

 tained in four longitudinal cavities, two on each side of 

 the median line of the anther, or, in comparatively rare 

 cases, in two cavities, one on each side of the median 

 line. The form of the anther is often materially affected 

 by the dilatation of the tissue of its median portion inter- 

 vening between the pollen-cavities. This dilatation is 

 generally more marked at the base of the anther than at 

 the apex, thus determining more or less divergence below 

 of the pollen-cavities, which in extreme cases of basal 

 divergence (Deadnettle) are actually brought end to end, 

 or indeed (Salvid) wholly separated from each other. 



The dehiscence of the anther, by which the pollen is 

 liberated, is usually longitudinal, and due to the rupture 

 of the septum separating the contiguous pollen-cavities on 

 the same side of the anther, the outer walls at the same 

 time receding more or less from their previous line of 

 attachment. In the case of anthers in which there is but 

 one pollen-cavity on each side, the dehiscence is along 



