Mr. Hassall on the Structure of the Pollen Granule. 95 



plants, which has but one envelope ; but Fritzsche has asserted, 

 according to Lindley, that these plants have both an extine 

 and intine. Fritzsche also states, that in Cauliniafragilis, Zan- 

 nichellia pedunculata, Zostera marina, and Naias minor, the 

 pollen has really nothing but the intine present. 



That there really are two coatings to the great majority of 

 pollen granules does not admit of a doubt ; while a third mem- 

 brane, intermediate between the extine and intine, has been 

 noticed, first by Mohl and subsequently by Fritzsche, who calls 

 it exintine. Mohl observed it in the pollen of Taxus, Juni- 

 perus, Cupressus and Thuja ; and Fritzsche finds it not only in 

 these plants, but also in Pinus, Cucurbita Pepo, and Tigridia 

 Pavonia ; while Mr. Giraud* states (in the third volume of the 

 ( Annals and Magazine of Natural History/ p. 127) that he 

 has noticed it in the pollen of Crocus vernus. To these I may 

 add the pollen of the different species ofBanksia and Dryandra 

 as possessing a third membrane, as well as the following list of 

 plants, Fuchsia fulg ens, F. cylindrica, F. thymifolia, F. gracilis, 

 and F. coccinea, Stachytarpheta mutabilis, Tilia americana, 

 Calothamnus villosus, Zizyphus Paliurus, and probably also 

 Grevillea linearis; Hakia pedunculata, Erythrina laurifolia, 

 Didiscus cceruleus, Fumaria officinalis, and all other species of 

 Fuchsia. It is necessary to observe great caution in deciding 

 upon the presence of a third membrane, as an appearance is 

 frequently observed which might mislead ; it arises from the 

 entrance of water within the sac of the intine, separating the 

 fovilla from it, forcing it inwards, and giving it a very denned 

 margin. 



At the commencement of this inquiry, I was induced to con- 

 sider that the reticulation observable on the pollen of Pancra- 

 tium, Armeria, Statice, Passiflora, &c. constituted the basis of 

 a distinct membrane, and in the figures of these 'which will 

 follow it is so represented. To this opinion I was led by no- 

 ticing the raised appearance which it presents, especially 

 round the circumference of the granules, as well as from the 

 circumstance of the ends of each grain of pollen in Pancra- 

 tium being destitute of the reticulation ; but it is more cor- 

 rect, perhaps, to regard this reticulated appearance as pro- 

 duced by the apposition of the cells of which the extine is 

 formed in these instances. 



Fritzsche also speaks of a fourth coat, which is next the ex- 

 tine, and which he calls intextine, as belonging to the pollen 

 of Clarkia elegans and other Onagrarice. Of the existence 



* Mr. Giraud, in the same communication, mentions having seen small 

 opake particles on the surface of the pollen grain of Polemonium cceruleum, 

 which exhibit a peculiar motion when the granules are placed in water. 



