582 The American Naturalist. (July, 
NATURAL IMPULSES. 
By W. BERNHARDT. 
There is a mystery existing in nature, inaccessible to human 
reasoning, as scarcely another one, although the phenomena 
connected with it are amòng the best known to us and of daily 
occurrence. When comparing a grain of mustard seed and 
one of poppy seed we even with the help of a magnifying 
glass cannot detect anatomical differenges of any concern. 
Each of them eneloses two cotyledons, i. e., the first leaves de- 
veloping in germination ; moreover, it contains a radicle and 
the beginning of a stem, both located between the cotyledons. 
Structure and appearance of these primitive organs are very 
similar in both seeds, and yet what a difference between a 
grown mustard anda poppy plant! Not only flower and fruit 
but the whole plant assumes a particular shape and character 
differing externally as well, as in chemical constituents. We 
are forced to believe, that the cells, from which both plants 
originate, are endowed with a disposition forcing the growing 
organs to assume certain forms in accordance with a certain ex- 
change of matter. 
Such a disposition or plan of structure is inherent to every 
germ of plant andanimal. Not the strongest microscope, nor 
any other means of observation have enabled us to ascertain 
the matter and processes upon which variation of development 
depends; only this much has been established, that the faculty 
is particular to the germ itself, the forms resulting from the 
growth of a certain kind of germ invariably manifesting the 
same characters, independent from external influences. Soil, 
climate and light certainly modify the thriving of a plant, and, 
when unfavorable, can even prohibit growth, but the plant re- 
sulting nevertheless invariably shows the characters of the 
species to which it belongs. Neither in animal nor in plant, 
has domestication or horticulture ever generated a new spe- 
cies. 
