436 M. A. Kerner on (he Protection of Pollen. 



short perianths and very long stamens — in a word, flowers 

 in which the pollen is completely exposed. 



Some plants which seem at the first glance to form an ex- 

 ception to the general rules above laid down, when attentively 

 examined really serve to confirm them. The Ericce, for 

 example, present the anomalous combination of a pulverulent 

 pollen with a coloured perianth producing nectar. But here, 

 just as in plants with coherent pollen, fecundation is impossible 

 without the intervention of insects. In fact the anthers only 

 open by two pores placed laterally at the apex of each cell ; 

 at the moment of flowering they are applied to each other by 

 their lateral surfaces so as to close all issue for the pollen. 

 To enable the latter to issue it is necessary that an insect 

 entering the flower should produce a shock upon one stamen, 

 which separates from its neighbours, lets fall a few grains of 



f)ollen upon the visitor, and then resumes its place. Some 

 ittle appendages which are developed at the base of the anthers, 

 and bar the passage of the insect, are exactly destined to pro- 

 duce the required movement. 



Analogous peculiarities occur in some Boragineae of the 

 genera Cerinthe and Onosma. 



Certain Salices, of which the pollen, although more or less 

 coherent, is not at all protected, remedy this by producing an 

 enormous quantity of pollen, and by prolonging their flowering 

 for a very long time (a circumstance which recurs with the 

 same signification in many Umbelliferee, Cruciferte, and Saxi- 

 fragaceee). Sometimes, also, parts of the inflorescence which 

 are already withered become a protection for those which are 

 about to open. 



We may remark also among heterostylous plants, such as 

 the Primulce, Pulmonarice^ &c., a marked tendency to di- 

 morphism of the perianth. It is more amply developed in the 

 form with long exserted anthers, where the protection of the 

 pollen is taore difficult. 



M. Kerner concludes his interesting memoir by some con- 

 siderations on the probable origin of the species with coherent 

 pollen, in which we shall not follow him : they do not appear 

 to us to be necessarily connected with the preceding ; and the 

 ideas of the author merit a discussion of which space will not 

 permit the introduction here. These pages suffice to show the 

 object and utility of the infinite variety of form of the floral 

 organs. 



