34 2 



THE POPULAR SCIENCE MONTHLY. 



can shore. . . . Kerner has seen a lake in the Tyrol so covered 

 with pollen that the water no longer appeared blue. . . . Mr. 

 Blackley found numerous pollen grains, in one instance twelve 

 hundred, adhering to sticky slides, which were sent up to a height 

 of from five hundred to a- thousand feet by means of a kite, and 

 then uncovered by means of a special mechanism." The so-called 

 showers of sulphur which have at times visited various cities, 

 notably St. Louis, are nothing but clouds of yellow pollen blown 

 from pine or other forest trees from some distant place. Perhaps, 

 out of millions of grains thus scattered far and wide, only a single 

 one may be of service. 



As if to compensate for this expenditure of pollen in some 

 plants, there are others in which the amount is very limited, and 

 where nearly every grain is made to count. These are known as 

 cleistogamous flowers, a term applied to those which always 

 remain in the bud. These flowers are found in plants belonging 



to about sixty different genera of various orders, 

 and generally in those species which at the same 

 time produce the normal and consjncuous flow- 

 ers. These large blossoms are often sterile, and 

 the plant must depend on the cleistogamous 

 flowers for its seed. In the wood-sorrel (Oxalis 

 acetosella), these flowers have each about four 

 hundred pollen grains ; the touch-me-not ( Ivi- 

 jxttiens) has only two hundred and fifty, and 

 some violets only one hundred. Even before 

 leaving the anther cells the grains in these 

 cases have protruded their pollen tubes ; these seek the pistil and 

 penetrate to the ovules. 



It might perhaps be supposed that, as the seed can be produced 

 so easily, all plants would have cleistogamous flowers. But here 



Fig. 9. Barberry. /, 

 filament ; a, anther ; 

 , stigma ; p, pollen. 

 (After Lubbock. ) 



Anther 

 p, processes 



Fig. 10. Corolla of Kalmia, (After Gray.) 



Fig. 11. Erica tciralix,~wnn Pendent An- 

 thers and Processes. (Alter Lubbock.) 



comes into play the fact that continual close fertilization is a great 

 detriment and not a benefit, and that it is better in the end that 



