ESSENTIAL ORGANS. POLLEN. 201 



(fig. 308); at other times those in the ulterior, as in Luhea (fig. 316, 

 2 fa). When the stamens are in two rows, those opposite the petals 

 are usually shorter than those which alternate with the petals. 



419. It sometimes happens that a single stamen is longer than all 

 the rest. In some cases there exists a definite relation, as regards 

 number, between the long and the short stamens. Thus, some flowers 

 are didynamous (3<?, twice, and StW^/f, power or superiority), having 

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

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

 occurs in Labiate and Scrophulariacese (figs. 344, 346.) 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. 345), and give rise to tetradynamous (rsr^tisj four, and BtW^/f, 

 power or superiority) flowers, as in Crucifera3. 



420. Stamens, as regards their direction, may be erect, turned in- 

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

 called declinate (declino, I bend to one side), as in Amaryllis, Horse- 

 chestnut, and Fraxinella. 



421. 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. 321), are sur- 

 rounded by a fibro-cellular en- 

 velope, c PI and within this are 

 produced larger cells, u p, con- 

 taining a granular mass (fig. 348, 

 1), which divides into four min- 

 ute cells (fig. 348, 2), around 

 which a membrane is developed, 

 so that the original cell, or the 

 parent pollen-utricle, becomes re- 

 solved by a merismatic division 

 (f 24) into four parts (fig. 348, 

 3), each of which forms a granule 

 of pollen. The four cells continue 

 to increase (fig. 348, 4), distend- 

 ing the parent cell, and ulti- 

 mately causingits absorption and 348 

 disappearance. They then assume the form of perfect pollen-grains, 



Fig. 348. Development of the pollen of Viscum album, or the Misletoe. 1. Two pollen-cells 

 or pollinary utricles filled with granular matter. 2. Four nuclei produced in this matter. 3. 

 Separation into four masses, each corresponding to a nucleus or a new utricle. 4. Pollenic or 

 pollinary utricle containing three separate vesicles in its interior. 5. Two of the latter, or the 

 young pollen-grains, removed from the mother-cell or utricle. 6. The grains of pollen in their 

 perfect state. 



