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



only small apertures in the surface of the now smootli extine, but 

 the pollen tubes do not pass through these. See fig. 32, 33. 

 Canna Occidentalis. C. Indica. 



ZlNGIBERACEjE. 



Extine covered with spines, which are permanent. 



Roscoea purpurea. 



Extine smooth. 



Hedychium Gardnerianum. H. flavescens. H. coronarium. 



VASCULARES. 

 EXOGENS OR DICOTYLEDONS. 

 Gymnosperms. 

 Conifers or Pinace^e. 

 Pollen grain kidney-shaped, and according to Fritzsche furnished 

 with three membranes ; extine cracking to admit of the emission of 

 the pollen tubes. See fig. 34, 35. 



Pinus sylvestris. Pinus Nova Zealandica. 



P. Pinaster. P. Tseda. 



Pollen granule circular, furnished with three membranes and 

 pollen tubes escaping by the rupture of the extine, as in the pre- 

 vious instance. 



Juniperus communis. J. Sabina. 



Taxace^e. 



Pollen granule similar to that of Juniperus. 



Taxus baccata. 



Angiosperms. 



DlCARPOS^E. 



Jasminacejs, Oleace^e, and Loganiace^e. 

 Pollen grain in its dry state of an elongated form, trilobate, each 

 lobe being separated from the others by a fissure passing through the 

 extine ; in water becoming spherical or triangular and emitting three 

 pollen tubes ; this change of form results from the approximation of 

 each end of the granule, occasioned by the imbibition of the fluid 

 surrounding it. 



Obs. — As the above type of pollen granule occurs hereafter in 

 families not allied to the above, in order to avoid the repetition of its 

 characters, just enumerated, the term cylindrical will be employed to 

 designate it when again met with. Although the same type of gra- 

 nule is of frequent occurrence, it is not to be inferred that it agrees 

 either with that of the above orders or any others in its exact form 

 or size, which varies considerably. It is to be regretted that the 

 size of all granules of the above form has not been ascertained. 



Jasminum odoratissimum. Olea europsea. 



Ornus europaea. Gsertnera racemosa. 



Syringa vulgaris. 



ApOCYNACEjE. 



Primary form of pollen granule cylindrical, very large, but when 



f 



