Mr. Hassall on the Structure of the Pollen Granule. 545 



smaller end of the figure ; but one pollen tube, which issues from the 

 larger extremity of the granule. The entire figure bears a rude re- 

 semblance to an acorn when in its cup. PI. XIII. fig. 1. 



Isolepis Holoschcenus. Scirpus capitatus. 



I. romana. Carex tomentosa. 



Cyperus longus. C. CEderi. 



Scirpus atrovirens. C. prsecox. 



S. carinatus. C. acuta. 



S. triqueter. 



The pollen grain of the following plant resembles that of the next 

 order in every particular but size. See fig. 2. 



Papyrus Antiquorum. 



Graminace^e. 



Pollen granules separate, circular at first, but on the emission of 

 the single pollen tube with which each grain is furnished generally 

 becoming ovoid, the larger end corresponding to that from which 

 the pollen tube issues ; extine containing a distinct circular aperture 

 for the escape of the pollen tube, which aperture is said by Fritzsche 

 to be provided with a valve, of which I have not been able to detect 

 the smallest trace. PI. XIII. fig. 4. 

 Dactylis glomerata. Triticum hibernum. Zea Mays. 

 D. abbreviata. Lolium perenne. Zizania aquatica. 



Sesleria elongata. Avena fatua. Andropogon furcatus. 



Poa fertilis. Aira vaginata. Panicum palmifolium. 



Elymus striatus. Spartina juncea. Phragmitis communis. 



E . sabulosus. S. cynosuroides. Arundo littorea. 



Triticum rigidum. 



Spadicos^e, 

 Typhacejs. 



Pollen grains united in fours, generally disposed upon the same 

 plane, and each emitting a single pollen tube. See fig. 5. 



Typha latifolia. 



AltACEjE. 



Called. 



Pollen grain, when dry, in outline describing a parallelogram, very 

 flat ; in water it changes to an ellipse, emitting a pollen tube from 

 each extremity. See fig. 6. 



Calla palustris. 



Pollen grain of an elongated ovoid form, bearing some resemblance 

 to a flask. Extine apparently without any provision for the pollen 

 tube, which escapes from the small end of the figure by the rupture of 

 that membrane. See fig. 7. 



Calla sethiopica. 



Hypogynos^e. 



JuNCE^E. 



Pollen granules united in fours, three being placed upon the 



