Notes on Pollen. By Lord Avehury, 479 



The Primulaceas also present several types : ellipsoid, triangular, 

 or sometimes quadrangular, rhomboid, with rounded lobules, or 

 with the furrows on the angles, oblong, barrel-shaped with six, 

 seven, or eight (or ? nine) ridges. It would seem, however, that 

 there are only three pores. 



I may also mention the Convolvulacese, which have at least 

 four quite distinct types : — 



1. Ellipsoid. 



2. Barrel-shaped, with several ridges. 



3. Hemispherical. 



4. Spherical, spiny. 



5. Spherical, faceted, smooth. 



Other orders presenting various types are Lentibulariaceae, 

 Bignoniacese, Scrophulariaceas, Verbenace^e, and others. 



In the Labiatse there are as many as ten forms ; even in the 

 single genus Stachys there are at least four types. 



Mentha is remarkable for having sometimes spirally-twisted 

 pollen. 



The Coniferse also present some ten different forms. 



In most cases the pollen of each species is very uniform, but 

 there are not a few in which the forms vary considerably. Some- 

 times this appears merely to result from some of the pollen being 

 imperfect. In others the position in which it happened to lie may 

 have affected the manner in which it subsided on shrinking. Cases 

 of such variety occur in Ranunculus, Rosa, Ruhus, and Veronica. 



Cultivation seems in some cases to produce considerable dif- 

 ferences in the pollen. Thus A. W. Sutton, in his Memoir on 

 Sola7iu7n* says : — " I find that the pollen-grains of all these wild 

 species are of one particular shape, namely, oval or elliptical, 

 whereas the pollen-grains of all the cultivated potatoes which 1 have 

 examined are very irregular in form and size, and possibly de- 

 generate." 



In some Sweet Peas f tJiere are two forms of pollen-grains, viz. 

 elongated and round, the former being " dominant." 



Again, the size is generally very uniform, but in some species, 

 as, for instance, in some of the Crocuses, there are considerable 

 differences in this respect. 



Mohl, in 1834, J not unnaturally concluded that it was im- 

 possible to obtain any information as to the structure of pollen 

 by mean;- of sections ; l)ut the improvement in mechanical appli- 

 ances between 1834 and 1860 enabled Schacht § to obtain sections 

 which seem to indicate (see, for instance, pi. xviii. fig. 35) that the 

 extine is thinner at the furrows. At the same time, the section 



* Pimnett, Mendelism, 2nd ed., p. 63. + Journ. Linn. Soc, 1908, p. 449. 



X Uber d. Bauein. Pollenkorner. Pringsheim's Jahrb., 1860. See also Biourge : 

 La Cellule, 1892. § Uber. d. Bau und Formen des Pollenkorner. 1834. 



