116 Vegetable Physiology. 



VEGETABLE PHYSIOLOGY. 



NUMBER FOUR. 



In the preceding articles we have described what are call <\ 

 the Elementary Organs of plants, or those whose nature i 

 disclosed by the aid of tbe microscope, and we now come 

 those various combinations of these, which are called Com 

 pound Organs, or simply, Organs, and which have been al- 

 ready mentioned as being divisible into Organs of Nutrition 

 and Organs of Reproduction. These do not all exist in every 

 plant, nor do they in any case show themselves all at once 

 but are developed successively, and sometimes are transformed 

 into each other. To obtain a general idea of them, it will be 

 proper to follow the progress of growth in some common plant 

 from the period when the seed begins to germinate, to that at 

 which it produces its own seed. 



In every seed is contained within the envelopes, a small or- 

 ganized body, called the Embryo. When germination lias com- 

 menced, this body swells, bursts its covering, and shoots out 

 into two parts, one of which penetrates into the ground, and 

 the other rises into the air. The descending part is called the 

 radicle, and ultimately becomes the root. The ascendin« part 

 is the plumule, or caulicle, and is the rudiment of the stem 

 leaves and flowers. From the point of junction of the plum- 

 ule and radicle, proceed laterally one or more appendages, 

 which are the cotyledons, and are the first leaves of the plant. 



When the root has attained its full growth, it usually be- 

 comes a fleshy body, variously branched, and furnished with 

 fibrils, or rootlets, having spongioles at their extremities, by 

 which nourishment is drawn from the soil. The plumule shoots 

 up into a stem, which subdivides into branches and twigs. 

 The Leaves are flattened, expanded organs, generally of a 

 green color, which absorb nutritious fluids from the atmosphere, 

 and exhale others. 



After them appear the Flowers, which decay and fall off, 

 except the part containing the seeds, which continues to grow! 

 and forms the Fruit. Thus the essential organs of plants may 



