ESSENTIAL ORGANS— POLLEN. 



229 



a viscous matter, surrounding the pollen-grains, as in Onagraeese. 

 In Orchideous plants the pollen-grains are united into masses or 

 poUinia (fig. 387), by means of viscid matter. In Asclepiadacese 

 (fig. 385) the poUinia are usually united ia pairs (fig. 386 b), 

 belonging to two contiguous antherine cavities ; - each pollen-mass 

 having a caudicular appendage, ending in a common gland, by means 

 of which they are attached to a process of the stigma (figs. 385 p, 

 and 386 p). The poUinia are also provided with an appendicular stami- 



Fig. 381. 



Fig. 382. 



Fig. 380. 



Fig. 383. 



Fig, 384. 



nal covering (fig. 385 p). Pollinia in different plants vary from two 

 to eight. Thus, there are usually two in Orchis, four in Cattleya, 

 and eight in Lselia. The two pollinia in Orchis Morio, according to 

 Amici, contain each about 200 secondary smaller masses. These 

 small masses, when bruised, divide into grains which are united in 

 fours. In Orchids each of the pollen-masses (fig. 387) has a pro- 

 longation or stalk, called a caudide (cauda, a tail), which adheres to a 

 prolongation at the base of the anther, called rostellum (rostellum, a 

 beak), by means of a viscous gland (fig. 387 g), called retinaculum 

 (retinaculum, a band or rein). The gland is either naked or covered. 



Fig. 380. Development of the pollen of Viscum album, or tlie Mistleto. 1. Two pollen- 

 cells or pollinic 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. Pollinic utricle containing three separate vesicles in its anterior. 5. Two of the latter, 

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

 in their perfect state. Fig. 381. Pollen of Periploca graeoa, showing four grains aggluti- 

 nated together. Fig. 382. Pollen of Inga anomala. The grains united in multiples of four. 

 Fig. 383. Pollen-grain showing the extine covered with small punctations. Fig. 384. 

 Pollen-grain with the extine covered with granulations. 



