1058 TnA.xsACTwxs of tite Amehican Institute. 



Pollen Uxt>er the Microscope. 

 In a paper read before the Manchester (England) Literary and Phi- 

 losophical Society " On Pollen, considered as an aid in the difi'eren- 

 tiation of species," the author, Charles Bailey, Esq., draws attention 

 to four points, in one orother of which pollen grains of plants belong- 

 ing to the same genus may be found to differ from each other. 



1. Form. — It has long been noticed that certain types of pollen are 

 characteristic of the natural order to which the plants that produce 

 them belong. This statement, however, must be accepted with limi- 

 tations ; the composite, for instance, have three or four well-marked 

 types, represented by the beautifully sculptured pollen of the chic- 

 cory, the minute oval spiny pollen of the asters, calendulas, cacalias, 

 &c., and another form wholly destitute of spines, as in the c^ntaurea 

 scdbiosa. There are, beside, other natural orders where similar 

 variety occurs. But differences of form are met with in plants of the 

 same genus, by which the one species or the other is readily marked 

 off by its pollen. 



2. 2farJchigs. — Here, again, there is endless variety, and a bound- 

 less field for the researches of tired-out, dot-and-line hunters of diatom 

 valves. 



3. Dimensions. — Some instances of differences observable in the 

 size of pollen grains have already been published by Prof. Gulliver, 

 whose measurements of the pollen of various species of ranunculus 

 show the help that may be derived from this character. 7?. arve7isis 

 is nearly twice the size of i?. hi/'suius, their dimensions being respec- 

 tively 1.470 and 1.888 of an inch. 



4. Color. — This is not so reliable a cliaracter for differentiation as 

 the others noticed, since species differ among each other accoi'ding to 

 the soil, &c., of the place M-here they liave grown. He remembered 

 gathering, some years ago, near Ashbourne, Derbyshire, a variety of 

 steUaria holostea^ having a dark purple pollen instead of the ordinary 

 pale yellow. Some objection may be raised to any reliance being 

 placed upon the dry shriveled up grains of lierbaria specimens, suqIi 

 specimens being in most cases the only ones obtainable for purposes 

 of investigation ; but the structure of pollen is such as to bring into 

 greater prominence tlie pores, folds, valves, and otlier markings which 

 are met witli on their surface after the grains have collaj)sed by the 

 discharge of their contents. 



In regard to the mounting of tlicse objects for the microscope thcj 

 show to the best advantage Avhen put up perfectly dry; the cells 



