162 The Ottawa Naturalist. [Mar. 



The pollen grains of a stamen taken from a plant belonging 

 to a good species, are all uniform as to size and general appearance. 

 When examined in a drop of water under a microscope mag- 

 nifying 200 to 500 times they appear opaque and of a dull 

 grayish colour, owing to the fact that they are filled with a rich 

 and slightly granulated protoplasma. 



The opaque appearance of the pollen grains and also their 

 uniformity are characters which can be observed not only on 

 living plants but also on pressed material which has been kept 

 dry for many years. 



The appearance of the pollen, developed by a hybrid plant, 

 is quite different. In the first place, the pollen grains are far 

 from uniform in size and shape. Only a few reach the size 

 of those of a good species, the majority being much smaller. 

 They appear irregular in outline, are often shrunken and always 

 of a bright colour. Examined under a microscope with a low 

 magnification, say 100 times, the pollen from a hybrid violet 

 gives an impression of emptiness and sexual incapacity. Exam- 

 ined under higher magnification, most of the pollen grains prove 

 really, to be empty or filled with a watery content. Even 

 those grains which, under lower magnification, appear to be 

 fairly normal, prove to be filled with a very poor and watery 

 Drotoplasma, and are therefore almost transparent. 



The percentage of good sized grains in pollen of violet 

 hybrids varies with the combination of the hybrid. The closer 

 the species from which a hybrid has been formed are related 

 to each other, the less degenerated becomes the pollen of the 

 hybrid. Those hybrids, however, which are formed from system- 

 atically widely separated species, have an extremely poor 

 pollen, the percentage of evidently wholly useless pollen grains 

 often running as high as 95 per cent or more. 



The sterility of the pollen in the petaliferous flowers of 

 hybrid violets is, briefly, just as marked as the sterility of the 

 capsules of the cleistogamous ones and consequently furnishes 

 an equally excellent means whereby, in doubtful cases, the 

 hybrid nature of violet plants can be ascertained. 



The fact that hybrids between distinct species of violets 

 show reduced sexual capability, should evidently be of great 

 assistance to students endeavouring to reach a clear under- 

 standing of the systematic relationships of closely allied forms, 

 inasmuch as the sterility or fertility of intermediates between 

 such forms may decide whether the forms in question represent 

 distinct specific units or merely are varieties of one species. 



This question will, however, not be further discussed 

 in the present paper. 



