395 



*** All the following figures of pollen are taken, with scarcely any alteration, 



from Purkinje, and are drawn to the same scale, so that their relative sizes 

 are shown. 



Fig. 12. Pollen of Stratiotes aloides. , Fig. 23. Pollen of Cineraria niaritima. 



13. Calla sethiopica. 24. Sal via interrupta. 



14. Elymus sabulosus. 25. Stachytarpheta 



15. Avena latifolia. mutabilis. 



16. Scirpus romanus. 26. Polygala spinosa. 



17. Pancratium declina- ; 27. Heracleum sibiri- 



tum. cum. 



18. Populus alba. 28. Acacia lopliantha. 

 1 0. Mirabilis Jalapa. 29. Iresine diffusa. 



20. Urtica dioica. 30. Fuchsia coccinea. 



21. Armeria fasciculata. i 31. Scorzonera radiata. 



22. Plumbago rosea. j 



Fiy. 32. Grains of pollen of Gesnera bulbosa emitting their tubes, magnified 

 180 times. The tube is of extreme tenuity, and may be withdrawn from 

 the stigmatic tissue with great facility. Masses of granular matter may be 

 seen descending the tubes at irregular intervals. 



Fig. 33. A grain of pollen of the same plant, with its tube magnified 500 tunes : 

 this shows that the tube is an extension of the outer membrane of the grain 

 of pollen, if the latter was coated by more than one. The granular matter 

 is seen passing down the tubes, and quitting the grain of pollen, which 

 finally becomes a transparent empty vesicle. 



Fig. 34. Grain of pollen of Datura Stramonium, emitting its tube ; after 

 Brongniart : a, pollen-tube. 



Fig. 35. Grain of pollen of Ipomoea hederacea, emitting its tube ; after 

 Brongniart : a, pollen tube. 



Fig. 36. Mode in which the pollen acts upon the stigma in (Enothera biennis : 

 a a, pollen tubes; b b, tissue of the stigma into which these tubes penetrate; 

 after Brongniart. 



Fig. 37. Mode in which the pollen acts upon the stigma in Antirrhinum majus ; 

 after Brongniart. The pollen sticks to the surface of the stigma, and the 

 tubes plunge down between the utricles of cellular tissue, of which the 

 stigma consists. 



Fig. 38. A grain of pollen of the same plant with its tube, more highly magnified: 

 a, the pollen tube. 



PLATE V. 



Fig . 1 . Vertical section of the ovarium of Dictamnus albus : a, gynophorus, or 

 elongated base of the ovarium ; b, base of the style ; c, cavity where the 

 carpella have not united ; J, cell ; e, placenta, with ovula attached to it. 



/-'/'/. -. Transverse section of the same in a more advanced state, where the 



