228 ESSENTIAL OEGANS — STAMENS. 



and in the progress of growth become included, as in Geranium stria- 

 tum (fig. 379). Stamens also vary in their relative 

 lengths as respects each other. When there is more 

 than one row or whorl in a flower, those on the out- 

 side are sometimes longest, as in Eosaceae (fig. 339) ; 

 at other times those in the interior are longest, as in 

 Luhea (fig. 348, 2, fa). When the stamens are in 

 two rows, those opposite the petals are usually 

 shorter than those which alternate with the petals. 



It sometimes happens that a single stamen is 

 longer than all the rest. In some cases there exists 

 'Fie" 379 ^ definite relation, as, regards number, between the 



long and the short stamens. Thus, some flowers 

 are didynamous (dig, twice, b-jvafiig, power or superiority), having 

 only four out of flve stamens developed, and the two corresponding to 

 the upper part of the flower longer than the two lateral ones. This 

 occurs in Labiatse and Scrophulariacese (figs. 376, 378). Again, in 

 other cases, there are six stamens, whereof four long ones are arranged 

 in pairs opposite to each other, and alternate with two isolated short 

 ones (fig. 377), and give rise to tetradynamous (riT^ae, four, d{jvaf/,is, 

 power or superiority) fiowers, as in Cruciferse. 



Stamens, as regards their direction, may be erect, turned inwards, 

 outwards, or to one side. In the last-mentioned case they are called 

 declinate (declino, 1 bend to one side), as in Amaryllis, Horse-chestnut, 

 and FraxineUa. 



The Pollen. — The pollen or powdery matter contained in the 

 anther consists of small cells developed in the interior of other cells. 

 The cavities formed in the anther (fig. 353) are surrounded by a 

 fibro-cellular envelope, cp, and within this are produced large cells, 

 up, containing a granular mass (fig. 380, 1), which divides into four 

 minute cell? (fig. 380, 2), around which a membrane is developed, 

 so that the original cell, or the parent pollen-utricle, becomes resolved 

 by a merismatic division (p. 14) into four parts (fig. 380, 3), each of which 

 forms a granule of pollen. The four cells continue to increase (fig. 

 380, 4), distending the parent cell, and ultimately causing its absorp- 

 tion and disappearance. They then assume the form of perfect pollen- 

 grains, and either remain united in fours, or multiples of four, as in 

 some Acacias, Periploca grseca (fig. 381), and Inga anomala (fig. 382), 

 or separate into individual grains (fig. 380, 5), which by degrees 

 become mature pollen (figs. 380, 6 ; 383, 384). In Acacia ringens, 

 there are eight pollen-grains united ; in Acacia decipiens, twelve ; and 

 in Acacia linearis, sixteen. Occasionally the membrane of the parent 

 pollen-cell is not completely absorbed, and traces of it are detected in 



Pig. 379. Bud of polypetalous corolla of Geranium striatum, exhibiting the stamens, e e, 

 at first longer than the petals, p p. 



