488 Transactions of the Society. 



(reraniaceffi, Campaniilacepe, Lauracere, Scitamineas Aracese, in 

 CucurUta, some Amaryllidaceffi {Amaryllis Belladonna, Crinuni). 



The spines no doubt serve to entangle the pollen in the haii^s 

 of insects and thus facilitate its being carried from flower to 

 tlower. They would also help to attach the pollen more firmly to 

 the stiuma, which in species with spherical spiny pollen is generally 

 papillo'se. The spines being numerous and scattered over the whole 

 surface, the pollen retains its original spherical form. 



If, however, the spines are few the conditions are altered. 



Hemispherical Pollen. 



In some cases spherical pollen flattens on one side, and thus 

 assumes a hemispherical form. 



Cases of this form occur in Caryophyllacepe, Dipsacese, Pole- 

 moniaceffi, Convolvulus, Pedaliacea?, Verbenacese, Plantaginese, 

 Nyctagineffi, Amarantacese, Chenopodiaceffi, Hydrocharideaj, Ur- 

 ticaceffi, Cupuliferte, Graminese, etc. 



A flat side would perhaps be an advantage in giving the pollen 

 an increased power of adherence to the stigma. 



Faceted Pollen. 



Faceted forms occur among the Carophyllaceae, Papaveracefe, 

 Eibesiaceffi, Convolvulaceae, Chenopodiacea, Urticaceaj, Myricaceai, 

 Cupuliferae, Alismaceffi, Graminea^. 



These cases are as a rule spiny. If the spines are numerous, as 

 in the preceding section, the pollen retains its spherical form; 

 there is no reason why it should give way in some places more than 

 in others. On the other hand, if the spines are larger and fewer,, 

 each of them becomes the centre of a more or less well-marked 

 disk, and thus the pollen assumes a faceted form. 



Stthaqueous Pollen. 



Most pollen if placed in water swells and perishes. Some 

 plants, however, develop their pollen under water, and in such cases 

 it develops a peculiar form, becoming cylindrical and somewhat 

 eel-like. 



Cylindrical pollen occurs in Naiadacese and Zosteracese (Zostera), 

 as was long ago pointed out by Fritzsche.* 



On the Size of Pollen. 



Delpino nearly fifty years ago suggested that the larger size of 

 the pollen in the short-styled flowers of heterostyled plants is con- 

 nected with the greater length of the pistil, and consequently the 

 greater supply of matter needed for the development of the longer 

 pollen-tubes. 



* De Plantarum PoUine. Berlin, 1833, p. 18. 



