544 THE POPULAR SCIENCE MONTHLY. 



ranean, the young growing extremities of which are pt-otected by a 

 layer of tissue called the root-cap. The stem is the axis of the plant, 

 and is the part which bears the leaves, and includes those peculiar 

 growths, such as thorns, runners, tendrils, etc., which serve a special 

 purpose in the plant economy. The leaf is a lateral outgrowth from 

 the stem, and is usually a flat, green expansion, but may assume the 

 form of scales, highly-colored and strangely-shaped floral parts, etc. 

 The fact that the largest tree and the smallest herb are alike made up 

 of a greater or less number of these plant-niembers, as they are termed, 

 leads naturally to the thought that any mass of plant-tissue having a 

 root, a stem, and a leaf, may be a plant individual, and that, when a 

 number of these members are intimately associated together, a com- 

 munity of plant individuals is formed. This is the modern concep- 

 tion of a tree or shrub a living structure, which is the result of the 

 combined, harmonious, silent working of many generations of indi- 

 viduals. Out of the three members are made all the multiplicity of 

 forms and structures which meet our eyes as we look upon the higher 

 forms of vegetation. They all have a common origin in the apical 

 growing-points, and are indistinguishable in their earlier stages, but 

 become differentiated as they develop, and at last assume their char- 

 acteristic, mature forms. The growing-point of a stem [punctiim, 

 vegetationis) is a conical apex, a little below which the leaves appear 

 first as very slight swellings. By their more rapid growth than the 

 stem, they reach above the growing-point, and, folding over each other, 

 cover it more or less completely. As the stem elongates, the leaves 

 upon the older portion are gradually separated, and an ordinary stem, 

 with its leaves arranged at regular intervals, results. A bud is sim- 

 ply a young stem, with its undeveloped leaves. A developed stem 

 is a series of similar parts, those parts being a leaf with a portion of 

 the stem above and below it, each borne upon its predecessor, and in 

 turn bearing the next one in the series. These similar parts have 

 received the name pliyton^ and are very generally considered as the 

 individuals out of which a plant community is built up. The gardener 

 divides the young branches of the verbena, salvia, etc., into these phy- 

 tons, and places them in moist sand, where they soon begin an inde- 

 pendent existence, and in time reproduce their kind. In the operation 

 of grafting, a similar portion of a plant community of one variety is 

 given a fitting place for growth in another, and by its growth and 

 multiplication of phytons a new colony is established. With this 

 view a tree or shrub may form an individual part of a landscape, but 

 not in the same sense that one may speak of a cow or a horse. The 

 tree more nearly resembles a swarm of bees ; there is a similarity of 

 unity between a shrub and a hive. The larger part of the shrub is 

 made up of foliar units, with ordinary leaves fo.r the elaboration 

 gathering, so to speak, of the food for the whole community. These 

 are the loorkers and the neuters of the vegetable "hive." Other plant 



