184 



:\[ANITAL OF BOTANY 



rare oases the outer coat appears to consist of two, or even 

 three, layers; while in Zostera, Zannichellia, and some other 

 submersed aquatic plants, there is but one membrane, which is 

 of a similar nature to the intine. 



The intine is the innermost layer, and appears to be of the 

 same nature and appearance in all pollen-grains. It is usiiaUy 



Fis. 384. 



Fig. 385. Fig. 386. 



Fig. 387 





Fig. 384. Pollen ol Hollyhock (Allhcm rosea). — Fig. 385. Elliptical pollen 



of Milkwort (^I'oltigala). r. Extine. /. Slits. Fill. 388. The same poBeu 



viewed from above. Fig. :1S7, PoUeu-cell of Dactylis glomerata. After 



.lussieu. 



smooth, very delicate, and transparent, and is composed of un- 

 changed cellulose. 



The cHine is a hard thick resisting layer, and is liable to 

 great variation ; it is sometimes smooth, at other times marked 

 with little granular processes, or spiny protuberances {fig. 384), 



Fig. 388. 



Fig. 389. 



Fig. 390. 



Fig. 388. Pollen of the Passion-flower (FassiJIora), before bursting, o, o, o. 



Liil-like processes. Fig. 389. Pollen of the Gourd, at the period of 



bur-;tinff. o, o. Lid-like processes of the extine protruded by the projec- 

 tions, ^ ', of the intine. From Jnssieu. F/g. 390. Trigonal pollen of the 



Evening Primrose ( (Eaothera biennis). 



or reticulations (fig. 388). The nature of these markings is 

 always the same for the pollen of any particular species or 

 variety of plant, but varies much in that of different plants. 

 The extine is often covered by a viscid or oily secretion. The 

 colour of pollen-grains also resides in the extine. In by far the 

 majority of cases they are yellow, but various other colours are 

 also occasionally found ;,thuB they are red in species of Verhascum, 



