498 Transactions of the Society. 



A very interesting illustration is afforded by the genus Mira- 

 hilis. Kolreuter long ago noticed that 31. jalapa could be fertilized 

 by pollen of M. lo7igifiora, but that on the contrary M. longiflora 

 could not be fertilized by pollen of M. jalapa. Perhaps the explana- 

 tion may be found in the relative size of the pollen in relation to 

 the length of the pistil. The pollen of M. longijiora is 0*152- 

 0-232 in diameter, while that of M. jalapa is only 0-112-0 -188. 

 On the other hand the pistil of M. longiflora is 14 cm. in length, 

 while that of M. jalapa is 5 cm. or less. 



The pollen-tube of i/. longiflora could therefore have no difficulty 

 in reaching the ovule of M. jalapa ; while that of M. jalapa being 

 no doubt adapted to the length of its own pistil would be unable 

 to reach the ovules of M. longiflora. 



Nevertheless there are many cases as yet unexplained. In the 

 genus Hypericum, H. calycinuni, H. androsR'mim, H. humifuswrn, 

 H. patulum, H. perforatum have pollen of very nearly the same 

 size, yIq mm., but the lengtli of the pistil differs considerably, viz. 

 in H. humifusum 3-5 mm., in H. perforatum 6, in H. patulum 3, 

 in H. androsivmum 10, and in H. calycinum 17. 



In Solanum dulcamara the pistil has a length of 8-9 mm. and 

 the pollen is only \^^ (250T) i^-). while in S. nigrum the pistil is 

 only 4 mm. in length, and on the other hand the pollen measures 

 yIq- mm. Thus the pistil is half the length and the pollen four 

 times larger. 



The size of the flower (apart from the length of the pistil as we 

 shall see) does not appear to have much influence. The little 

 Euphrasia officinalis has pollen 0-06 mm. in length, though the 

 flower is only 5 mm. in diameter and 6 in length. 



It is clear therefore that the size of pollen does not depend 

 entirely on the length of the pistil. Evidently, however, it is a 

 factor in the case. Plants with long pistils as a rule have large 

 pollen. This is said to be the case also with those flowers which 

 open only for a day. 



I will now proceed to make a few remarks on the pollen of 

 some of our principal British Families. 



Eanunculace^. — The pollen is generally ellipsoid, rounded at 

 the end, with the usual three furrows. As a rule the pollen is 

 smooth or finely granular, but in some Anemones it is rugose or 

 warted. 



Ranunculus ficaria may be taken as representing the most 

 common type. When the anthers open the pollen grains are 

 spherical (fig. 7), but if the atmosphere is dry they subside in 

 about half-an-hour and become ellipsoid (fig. 8), obtuse at the ends, 

 bright golden yellow, glittering, very finely granular, viscid, but 

 gradually becoming dry and crumbling. The end view (fig. 9) is tri- 

 angular, with rounded lobules, and three narrow, but fairly deep, 

 furrows. The pollen grains vary somewhat in size from 0-034- 



