Dec, 1921] PATON — POLLEN AND POLLEN ENZYMES 473 



In summarizing he says: 



The enzymes present in the resting pollen grains are, therefore, chiefly diastase and 

 invertase, but their distribution is irregular, some containing one, some the other, and some 

 both. At the onset of germination usually the amount of both diastase and invertase is 

 considerably increased. . . . When the grain has lost the power of germinating the quantity 

 of diastase is materially decreased. 



The conclusions, as will be noted later, are not entirely in accordance 

 with the results of the present experiments. 



The Significance of Pollen to the Living Plant, and the Probable Role of 



the Pollen Enzymes 



A medium-sized Indian-corn plant produces about 50,000,000 pollen 

 grains. Cat tails (Typha), which produce about 60,000 flowers to the 

 average spike, shed enormous quantities of pollen. A near relative, the 

 elephant grass {Typha elephantina) of East India and New Zealand, yields 

 enough for the natives to use as a flour in bread- and cake-making. The 

 dense cloud of pollen from a pine tree has been photographed, and many a 

 camper has noticed the yellow powder staining the canvas of his tent when 

 dampness has moistened the grains. Liefmann (1904, p. 163) found 

 2,500,000 grains of grass pollen in one square meter. Yet so tiny and light 

 are these pollen grains that a small amount represents millions of grains. 

 Ulrich (1914) estimated 172,800,000 grains in one gram of ragweed pollen, 

 and Kammann (191 2) estimated 20,000,000 in one gram of timothy pollen. 

 Pollen grains are nearly omnipresent during the flowering season. One 

 would suppose from these figures that it is an easy matter to collect large 

 quantities of pollen, but it is really not easy. The winged grains of pine 

 pollen are blown away by the slightest breeze. Ragweed pollen cannot be 

 collected easily after nine o'clock in the morning. The grain of pollen is 

 surrounded by an oily envelope containing air. When this air is heated 

 by the sun it causes the floating away of the pollen, or the so-called "smok- 

 ing" of the ragweed. It is not easy to get enough for an experiment. The 

 fact that during three fourths of the year we have pollen grains always 

 with us makes it evident that if they have active enzyme action their im- 

 portance cannot be lightly overlooked. 



Pollen grains present many types of configuration. The commonest 

 forms are oval or spherical, but an extreme variation is seen in the extra- 

 ordinary filamentous pollen grains of eel grass (Zostera) and of another 

 water plant, Halophila. Although the grains differ greatly in shape and 

 in surface markings or finish, in internal structure they are very uniform. 

 They usually consist in the Angiosperms of two cells. One cell is purely 

 vegetative and gives rise to the pollen tube ; the other is the generative 

 cell. 



Pollen grains vary considerably in size. A very extensive list of both 

 measurements and descriptions of the pollen grains of many species and 

 families is given by Hansgirg (1897, pp. 17-76). 



