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



this difference observable between the pollen of the two grand 

 classes of the vegetable kingdom, but it will be further no- 

 ticed, that the more or less complex structure of the pollen 

 bears some reference to the station of the plant in these divi- 

 sions, especially in the monocotyledonous ; a fact hitherto 

 denied by all vegetable microscopists who have paid attention 

 to the subject, but one which can scarcely again be called 

 in question after the very conclusive evidence of its truth fur- 

 nished in the antecedent pages. 



The pollen granule of Cyperacece and GraminacecB is either 

 oval or spherical (the simplest forms in nature), and has 

 but a single pollen tube. Mounting a step higher to the Ty^ 

 phacece and Juncacem^ we meet with the same type and struc- 

 ture of granule ; but instead of being separate, as in the Gra- 

 minacece and Cyperacece, the grains are united in fours. In 

 Calla the form is oval, and a pollen tube issues from either end. 

 In the genus Butomus, in the Liliacece, Melanthacece, Brome- 

 liacece, Iridaceae, and Amaryllidacea, it is more complex ; each 

 grain is of an elongated shape, tapering almost to a point 

 towards either extremity, with a furrow running down one 

 side, from which, however, only a single pollen tube issues, 

 as in the Cyperacece and Graminacece. In Zingiberacem, Ma- 

 rantacece, and Musacece, the form of each granule again be- 

 comes very simple ; it is a perfect sphere, and the extine, 

 which is of great thickness, contains no provision in it for 

 the passage of the pollen tubes, but possesses the power of 

 cracking (a peculiarity met with only in the pollen of these 

 allied orders and that of the Taxacece and Conifer ci), and so 

 allowing of their escape. In Orchidece the granules are united 

 in fours, and are likewise of a very simple structure. 



The Taxacece and ConifercB, which, though usually placed 

 among dicotyledons, ought to be regarded as forming the con- 

 necting links between monocotyledons and dicotyledons, also 

 possess pollen of a very simple form and structure, but still 

 somewhat more complex than that of any of the preceding 

 orders. It is here for the first time that I have met with 

 the third membrane, which Fritzsche however mentions as ex- 

 isting in Tigridia pavonia, and Mr. Giraud in Crocus vernus^, 

 both monocotyledons. 



We come now to a class of plants decidedly exogenous, the 

 Jasminacece : here the pollen is much more complicated ; 

 when dry it is cylindrical, and 3-lobed ; in water it becomes 

 triangular and emits three pollen tubes ; while in Labiatce, an 

 order not very far removed from the preceding, it is 6-lobed 

 and furnished with as many pollen tubes. In the remaining 



* Mr. Giraud's papers on tlie structure of the pollen appeared in vol. ii, 

 p. 399. pi. XVIII., and vol. iii. p. 127 of this Journal.— Ed. 



