president's addeess. 123 



fore well raise the question — "Are such plants placed in their 

 true ^Natural Order ? A study of pollen may therefore assist 

 classification. 



PnoDircTiON OF Pollen. The pollen lies within each loculus, 

 at first a solid mass. This mass soon becomes cellular, and the 

 cells speedily develope into large mother-cells. Usually the 

 mother-cells divide, either at once or at twice, into four daugh- 

 ter-cells, which become free by the more or less perfect absorp- 

 tion of the primal wall of the mother-cell. These free-cells now 

 lie in the granular fluid of the anther loculi, which they gradu- 

 ally use up, so that when mature the loculi are filled with a 

 powdery mass of pollen grains. This is the normal mode of 

 production in temperate regions, but there are numerous devia- 

 tions. Thus, the primary mother-cells may be followed by 

 secondary, tertiary, and other mother-cells before the final stage 

 is reached ; the mother-cell wall may be only partially absorbed, 

 leaving strips of cell-tissue or masses of gelatine or gum ; the 

 mother-cell wall may remain whilst the daughter-cell walls are 

 absorbed, when the pollen will not be simple grains but aggre- 

 gates, usually of fours or threes. Hence pollen grains may be 

 simple or compound. They are mostly simple. The absorption 

 of the mother-cell walls may be only partial, for in absorption 

 the cellular tissue first passes into mucilage and then disappears. 

 The absorption is therefore imperfect when gum or wax remains, 

 equally as when strips or shreds are left. Degeneration of the 

 walls of the mother-cells actually produces dry threads or chains, 

 moist fibres, or a sticky mass ; — tufts of dry hairs or threads in 

 the Fuschias ; brittle and cellular-looking fibres, like delicate 

 branching zoophytes, in Lavandula vera, or like strings of beads 

 in Celosia cristata ; whilst in the Epilobiums and ^nothera 

 biennis they are so numerous, long, and pliant, that the pollen 

 grains hold together in felted masses. In other cases the threads 

 are distinctly sticky, as in the Arums, Azaleas, Heaths, and 

 Imentophyllums, where the pollen can be lifted out of the ripe 

 anther-sacs in strings, whilst in Passijiora c(srulea the pollen 

 leaves the anther-loculi in two rod-like strips, which, being 

 reddish, show up well on the yellow anthers. Tropical and 



