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



sections of orders, and that where it does not go so far as 

 this, it is to be rehed on as affording a character of at least 

 generic importance. 



Now with reference to the third assertion of Mohl, that in 

 some plants the same anther contains distinct forms of pollen, 

 I can affirm it to be wholly and without exception incorrect. 

 The only difference ever observed in pollen of the same spe- 

 cies arises either from the addition to the distinguishing type, 

 or subtraction from it — most frequently the former — of one or 

 more pollen tubes, generally of one ; an anomaly which is of 

 frequent occurrence in some species, especially in the follow- 

 ing, Stachytmyheta miitabilis, Rubus /ruflcosus, Nicotiana 

 Tabaciim, Solaniim tuberosum ; and those granules so changed 

 are to be regarded as malformations or monstrosities, of which 

 an instance is exhibited in fig. 50, Avhich represents a gra- 

 nule of Stachytarpheta mutabilis thus deform.ed. Every 

 organ and part of the vegetable and animal fabric is subject 

 to similar occasional departui'es from normal structure. 



When a number of flowers are placed together for some 

 time in a vessel, an intermixture of the pollen of each not un- 

 frequently occurs, so that Avhen that of any species is exa- 

 mined, more than one form of pollen granule may be observed ; 

 but no person would be so careless as to suppose for a moment 

 that these were derived from the same anther. 



These monstrosities are of very frequent occurrence among 

 hybrid species, particularly of the Fuchsia. In the^;?/re s))ecies 

 of Fuchsia each granule is furnished with either two or three 

 pollen tubes; now among the pollen ofi^. Standishii, a hybrid 

 between F.fulgens, whose grains of pollen have but two tubes, 

 and another species the granules of which have three tubes, 

 the greatest confusion seems to prevail, some of the gi'anules 

 having but two or three tubes, thus following the type of 

 either parent, \\ hile others have four tubes ; and many of them 

 appear altogether abortive, and consist of nothing more than 

 the extine, which does not even contain fovilla. Here then 

 a satisfactory reason is afforded why the seeds of hybrid spe- 

 cies should be so frequently unproductive, since they either 

 have not received the influence of the degenerated pollen at 

 all, or have so in an imperfect manner. 



The same form of pollen granule met with in one order 

 sometimes occurs in another separated from it by every point 

 of structure ; but when this does happen, most frequently a 

 difference either in the size of the granule, the number of 

 membranes which envelope it, or of pollen tubes which issue 

 from it, is observable ; and when no such distinction can be 

 discovered, the family in which it occurs may be so estranged 

 from that possessed of pollen of similar formation, as that it 



