THE UNIT IN PLANT-LIFE. 545 



individuals devote their energies to the production of new plant-units, 

 namely, the stamens the male units of the flowers which perish as 

 soon as their transient but important work of fertilizing the pistil is 

 accomplished ; these are the drones. The pistil is the central part of 

 the flower, and around which all the work of propagation converges 

 and the labors of the year culminate, and from which the new indi- 

 viduals, the seeds, go forth to develop into free and independent col- 

 onies. In several respects this pistil is queen of the congregated vege- 

 table units. 



There are some objections to the j^hytons being considered the 

 unit of vegetable life. The division of a plant may be carried be- 

 yond it, and life and growth of the parts still be maintained. Thus 

 buds may arise from petioles, or leaf-stalks, and from the veins of 

 the leaf, as in the ordinary propagation of the begonia, and very 

 strikingly in the bryophyllum. Buds may start from the Avoody bundles 

 of roots, as in the sweet-potato, poplar, or the cut stems of the elm, 

 willow, etc. These many cases of a seemingly spontaneous growth 

 have led to another definition of the plant-unit which is formulated 

 briefly as follows : A plant individual is that smallest part that can 

 grow when separated from its former place in a plant community, and 

 given the fitting conditions for growth by itself. In most cases this 

 " smallest part " is the phyton, or a portion of the stem with its leaf, 

 and the bud or growing point which it bears in its axil. This young 

 lateral bud, which is frequently so small as to be unseen by the naked 

 eye, is, in fact, the vitalized, undeveloped stem that is to increase in 

 size if growth takes place. The writer is of the belief that in this 

 growing-point the individuality of higher plants should be located. 

 If there are two buds upon the phyton, it seems proper to say there 

 are two individuals, as there are two distinct points of growth, and 

 two branches may result therefrom. 



If the phyton is to be considered as the plant-unit, we must seek 

 for another unit of life for those plants in which no phyton elements 

 exist. The unit of growth is the cell ; in it, either alone or in con- 

 nection with other cells, all the functions of life are performed. Cells 

 compose the growing tissue of every plant ; in them resides that vital- 

 ized substance called protoplasm, in which all life-changes take place, 

 and from which all structures are built up. 



Many of the lower plants are unicellular, as, for example, the com- 

 mon yeast-plant, bacteria, etc., among fungi, and the desmids and 

 diatoms among algoe. They increase in number by a simple division 

 of the cell into two, each half increasing in size and dividing as did 

 its parent. The individual among such plants is evidently the single 

 cell. As we pass a little higher in the scale of vegetable life, it is 

 found that though the cells are associated together in filaments, or 

 laminae, they are, in most respects, very independent, losing only a trifle 

 of their originality by being associated in the simplest form of a com- 



TOL. XIX. 35 



