Notes on Pollen. By Lord Avehury. 481 



2. Viscidity is an advantaoe. Insects cannot so readily carry 

 off dry pollen as that which sticks to them. When collecting 

 the pollen of the plantain {Pkmtago) bees have learnt to moisten 

 it with honey, and are thus able to collect it in packets, which 

 would otherwise not be possible. Hildebrand * observes that 

 the species of Cyclamen are at first entomophilous and then 

 anemophilous. In the earlier stage they are viscid, in the latter 

 dry. 



3. In many cases the anthers perform definite movements, as 

 in Salvia, Berber is, etc. 



As regards surface, most pollen may be said to be smooth, but 

 in many species it is spiny, in others knobbed, reticulated, covered 

 with long threads, etc. Knobs, tliough perhaps less effective than 

 spines, would to some extent serve the same purpose. 



As a rule, the pollen-gra'ns are separate, though often adhering, 

 in bunches ; but in some families the last cell-division is not com- 

 plete, and the grains are more or less closely united in fours 

 (tetrads). 



Tetrads occur in most Ericacese, Yacciniacese, some Droseraceae, 

 Onagraceae, Solanacese, Asclepiadacea?, Epacridacese, Orchidese ; in 

 Victoria, regia, Salpiglossus, Juncacem, JSmpctrum, Typha. 



In other cases the pollen-grains are attached in groups of 

 definite forms. In Acacia platyptera, for instance, twelve grains 

 are united into a square biscuit : four of the grains are in the 

 centre, each surrounded by a rectangular ridge, while the other 

 eight are arranged two on each side of the central square, but turned 

 round so as to show their ridges only. Some bundles, however, 

 contain eight grains only. In A. armctta and A. lineata the group 

 is circular : two grains in the centre and six ranged round them. In 

 Callianclra h/eviatocephala, also, it consists of eight grains, arranged 

 in a pyriform group. 



The advantage may be that, a number of pollen -grains being 

 carried together, many ovules may be fertilized. As the flowers 

 fade soon after pollination, many ovules might, unless enough pollen 

 were supplied at once, remain unaffected. Pollen-grains coming any 

 later would find themselves, like the foolish vii'gins, too late. 



Threads. 



Some pollen is held together, and no doubt adheres to the 

 pistil by long viscid threads. According to Kerner the sticky 

 substance is probably a mucilage formed i'rom the outer wall of the 

 pollen-tetrad, or from the broken-down walls of the mother-cells. 

 This provision occurs among Onagracea?, in Azaleas, lihododendrons, 

 Orchids, Asclepiads, etc. 



* Ber. Deutscb. Bot. GeseU., 1897. 



