Mr. Hassall on the Structure of the Pollen Granule. 571 



Fig. 43. Pollen granule of Mimulus guttatas. 



44. Shows the mode of union and structure of the pollen granules of 

 Salpiglossis atropurpurea. 



45. Pollen granule of Justicia variabilis. 



46. of Acanthus spinosa. 



47. of Thunbergia alata. 



48. of Eranthemum pulchellum. 



49. Represents the pollen granule of Stachytarpheta mutabilis. 



51, 52. Two views of the pollen granule of Monarda didyma : the first 

 represents it as it appears in its dry state ; the second, the change of 

 form which it assumes prior to the emission of the pollen tubes, and 

 which arises simply from the approximation of the two extremities of 

 the first figure (the resemblance of which to a melon is striking), and 

 the protrusion of the intine through the extine ; this approximation 

 being due to the operation of the principle of endosmosis. 



53, 54. Two views of the pollen granule of Symphytum officinale ; 53, 

 in its dry state ; 54, in its moist condition. 



Plate XV. 



Fig. 55, 56, 57, 58. Four views of the pollen granule of Borago officinalis ; 

 55, front view ; 56, side ditto ; 57. and 58. show the changes which it 

 undergoes on the stigma previous to the emission of the pollen tubes, 

 first becoming oval and subsequently circular. 



59. Pollen granule of Eutoca viscosa in its dry state. 



60. of Nemophyla insignis. 



61. of Armeria vulgaris. 



62. 63. Pollen granule of Plumbago caerulea in its dry and moist con- 

 ditions. A small valvular strip of membrane, not represented in the 

 figure, is placed over each of the three furrows. 



64. Pollen granule of Plantago lancifolia. 



65, 66. Pollen granule of Cynara scolymus ; 65, in its primary order, 

 and 66, in its secondary or moist condition. 



67. Pollen granule of Scorzonera hispanica. 



68, 69. Pollen granule of Eupatorium purpureum ; 68, in its dry, and 

 69, in its moist condition. 



70, 71. Pollen granule of Crucianella stylosa ; 70, in its primary, and 

 71, in its secondary condition. 



72. Shows the mode of union and structure of the pollen granules of 

 Oxyanthus speciosa. 



73, 74. Pollen granule of Burchellia capensis ; 73, in its primary, and 

 74, in its moist condition. 



75. Shows the structure and arrangement of the pollen granules of 

 Leehenaultia formosa. 



76, 77. The first figure represents the pollen granule of Campanula 

 pyramidalis, with the pollen tubes just emerging through the aper- 

 tures in the extine ; the second that of Campanula patula, with the 

 pollen tubes in the same condition. 



78. Pollen granule of Lobelia procumbens. 



79. of Cobaea stipularis. 



Plate XVI. 

 Fig. 80. Pollen granule of Collomia grandiflora. 



81. of Gilia tricolor. 



82. of Phlox Drummondii. 



83. 84. Pollen granule of Ipomopsis elegans. 



85, 86. of Convolvulus arvensis in its dry and moist 



conditions. 



2P2 



