38 POLLEN. 



views of some, from the membranous cells we before spoke 

 of as enveloping the nuclei, not being absorbed or des- 

 troyed ; and, according to others, from an actual grow- 

 ing together of the four grains, which is much stronger 

 in some genera than it is in others ; these smaller pollen 

 masses are connected to each other by a peculiar yel- 

 lowish sticky matter somewhat resembling birdlime. 



207. The forms of the individual grains of pollen are 

 very various ; perhaps the most common is the ellip- 

 soidal (6), a very complete example of which is seen at 

 (c), the pollen of Ruellia barlerioides. The spherical is 

 seen in the Coniferse (c?), and a lenticular with pro- 

 jecting corners at (e). Other forms are seen in the 

 same figure. 



208. The grains of pollen of most plants have their 

 coats composed of two membranes ; the outer one is 

 called the extine, aud the innermost the intine. Ac- 

 cording to some, in Coniferse and in few other plants, 

 there are three coats, and in (Enothera and Clarkia, often 

 four. Meyen denies, or rather doubts, this last state- 

 ment of Fritzche, from his own observations on the 

 same plants. 



209. The intimate structure of these coats, cannot be 

 said to be determined, many regarding them as cellular 

 tissue, others as homogeneous membrane : the latter 

 opinion appears, I think, the more probable. 



210. The external surface of pollen is very variously 

 marked in different species, as is seen in (fig. 37) ; in 

 most grains in which the development is longitudinal, 

 as at (i), there is a mark or furrow extending along 

 them from end to end, and in others, as at (k), there 

 are circular spots or marks upon their surface. These, 

 according to some, are openings of the external coat ; 

 according to others, mere thinnings of it. 



211. The matter contained within these coats, or 

 otherwise the contents of the grains of pollen, is called 

 the fovilla. It consists of a more or less thick and 

 transparent mucus in which two distinct kinds of bodies 

 are seen endowed with motion ; the larger of these 



