DISCURSIVE. 115 



CROSS FERTILIZATION. 



The production of seeds by the transference of pollen from the blossom 

 upon which it ripens to the seed germs of some other blossom, is called 

 cross-fertilization. The falling of the pollen upon the pistil of the same 

 flower is called self-fertilization. The prevention of self-fertilization is 

 secured by many wonderful devices, while cross-fertilization seems need- 

 ful, not only for the normal development, but even to the continuance of 

 the vegetable kingdom. Among other means to this preventive end is the 

 curious difference in time between the ripening of the pollen-sac and of the 

 seed germs upon the same flower. There is but one time in the history of 

 the pollen when it can fertilize the seed, that is when the pollen is entirely 

 ripe, but while its cadence has not yet begun. Also, the seed germ can 

 only be fertilized when it has reached, not passed, its proper stage of 

 maturity. Now, the critical moments of the due ripeners of germ and 

 pollen are seldom simultaneous in the flower. The pollen-sac discharges 

 its treasure to be insect-borne to some more mature blossom ; the seed 

 germ delays its ripening and awaits the Danae-shower from other laggard 

 bloom. Julia McNair Wright, in Science News. 



LIGHT INFLUENCES. 



In the earliest stages of life the little seedlings of most trees require 

 partial shade and are quite sensitive in regard to light conditions. Some 

 have such a small range of light and shade endurance that, while there 

 may be millions of little seedlings sprouted, they will all perish if some of 

 the mother trees are not removed and more light given; and they will 

 perish equally if the old growth is removed too suddenly and the delicate 

 leaf structure, under the influence of direct sunlight, is made to exercise 

 its functions beyond its capacity. 



STRUGGLING FOR LIGHT. 



Left to itself, as the forest grows up and as the individual trees develop, 

 each trying to hold its ground and struggling for light, there is a natural 

 thinning taking place, some trees lagging behind in growth and being 

 shaded out, until in old age only as many trees remain as can occupy the 

 ground without incommoding each other. This struggle among the in- 

 dividuals goeson during their entire life. Some few shoot ahead, perhaps 

 because of a stronger constitution or some favorable external cause, and 

 overtower their neighbors; these, lagging behind, fall more and more 

 under the shading influences of their stronger neighbors until entirely 

 suppressed, when they only vegetate until they die, while the struggle 

 continues among the dominant class and is never ended in a forest that is 

 utilized at the proper time by man. 



