84 



POLLEN. 



102 



103 



The connectivum often appears under modified forms. Some 

 of these we have ah-eady noticed, as in the sage. In the As- 

 clepias also the little liorns observed in the flowers of these 

 plants, are developments of the connectivun. Some- 

 times it is very much enlarged, as in fig. 102, at 

 others forked, as in fig. 103, at others form- 

 ing a crest, and again forming a cap-like 

 body articuhited With the apex. The po- 

 sition it occupies in these and other cases, 

 will enable the observer to determine to 

 what organ it is to be referred. 



Pollen. 



96. The pollen consists of exceedingly minute grains, 

 which, under the microscope, appear of various forms. In 

 some they are smooth and spherical, as in the Marvel of Peru ; 

 in others with an equatorial whorl of conical papillse, as in 

 the Hib sous grandijlorus ; in others angular, some nearly 

 square and of every variety of geometrical figure. It would 

 be useless to specify the great variety of forms under which 

 this substance appears, as it has, as yet, been made of little 

 practical importance in arranging plants, although so far as 

 we have made observations on this subject, we believe it might 

 in some cases be made a good specific character, and in others 

 a generic one of much importance. We have never found a 

 variation of form in the same species and in some extensive 

 genera, so far as we have examined them, the form is invari- 

 able. 



The student can scarcely find a field for more curious ob- 

 servation, if he has a good microscope, than is presented by 

 the pollen. The variety of beautiful forms it assumes, in dif- 

 ferent species, and the curious structure of the pollen grain 

 itself, present subjects of much interest. 



97. The term gemule has been applied to the pollen grains. 

 They enclose a fluid of molecular matter essential to the pro- 

 duction of the seed. The molecular formation may be beau- 

 tifully observed by sprinkling some pollen on the port-object 

 of the microscope, and dropping on it some diluted sulphuric 

 acid. The coats of some of the grains immediately burst, 

 and the contents of the grain are projected into the fluid, and 

 the molecules may be distinctly seen. The pollen has been 

 determined, by the most accurate observers, to consist of two 

 coats, at least, the outer and thicker one called the extine, the 



