Notes on Pollen. By Lord Avebury, 483 



given ])y Schacht* of a section of pollen grains of Foinciana j)^^- 

 cherrinia. I submit, however, that if contraction took place in the 

 first instance in accordance with mechanical principles merely, it 

 would gradually set up lines of weakness. 



The Holly presents a remarkable development of this form. 

 The pollen is oblong ellipsoid, with a deep central furrow, rather 

 opaque, and covered all over with roimd translucent knobs. The 

 small lobule lies on the other two. Some of the grains appear to 

 have the sides folded in, and then one end again folded in on the 

 top of the other two. 



Another extreme form is presented by the Honeysuckle {Loni- 

 cera peridymenum), where the areas between the furrows sometimes 

 subside so far that the pollen consists of three narrow longitudinal 

 ridges, each with the original furrow on the top. 



As a rule there is a so-called " pore " in each furrow. I say 

 " so-called," because it is confined to the exine, and the intine is 

 continuous, f 



In some cases, however, the furrows are numerous and seem 

 to have no relation to the pores. 



As a rule the furrows are on the faces of the lobes (fig. 9), but 

 in some species the furrow is on the ridge, which gives a peculiar 

 form to the pollen (figs. 11 and 12, Tropxolum). 



Such cases occur in some Scrophulariaceee, Labiatse, and Euphor- 

 biacese, in Tropmolum, Viola, Rhamnus, Vitis, Lonicera, Verbena, 

 Cistus, Dictamnus, Rhus, Saxifraga, Bryonia, Ardisia, and others. 



In these cases the end view is triangular, but in others, as for 

 instance Viola lutea, the pollen is brick -shaped (figs. 13 and 14) 

 and the end view is quadrangular. 



As a rule the ridges are horizontal, but in some (Thunbergia, 

 Mimulus) they are spiral. 



Dumbbell-shaped Pollen. 



Dumbbell-shaped pollen is very general in the Roraginese. It 

 also occurs for instance in some Umbelliferte, ScrophulariacetB, 

 Heemoridaceffi, Papilionacete {Mclilotns, Anthyllis, TrifoliuTn). 



The peculiarity of form seems due to the fact that the sub- 

 sidence due to contraction takes place transversely and not 

 longitudinally. 



Tliis again may be owing to the shortness of the furrows, or to 

 these being much deeper in the middle. 



Spherical Pollen. 



The spherical may be said to be the original and natural form 



* U. d. Bau ein. Pollenkorner, Pringsheim's Jahrb., 1860. 

 t Fritsche, De Plantarum Polline. Berlin, 1833, p. 10. 



