334 CIVIC BIOLOGY 



Law of heredity. Organisms tend to produce offspring like 

 themselves. Variation is as destructive as it is constructive. 

 It may give us the Spitz enburg apple, and the seeds of a Spitz- 

 enburg may revert toward the original wild apple. Heredity 

 is the force that enables us to conserve the gains supplied by 

 variation. Organic reproduction is of two kinds — asexual, or 

 vegetative, and bisex^lal. The asexual process is seen in 

 growth and simple division, as found among the bacteria, or 

 growth with budding, as in the yeasts. and in plants generally 

 and in many of the lower animals. In all this reproduction 

 we virtually have continuity of the organism, and this can go 

 on indefinitely with little or no variation. So buds, grafts, 

 cuttings (of stems or roots), layers, runners, Ijulbs, bulblets, 

 tubers, and, in short, all purely vegetative parts of plants 

 capable of reproduction carry the variety true to name. 

 This means that every bud on a Spitzenburg apple tree, 

 rooted in the ground or grafted into any kmd of apple 

 root or branch, will produce a true Spitzenburg tree, while 

 not a seed from all the Spitzenburg trees in the world might 

 be able to do this. Tliere is some talk, but little evidence, 

 that varieties tend to run out, or grow old, under bud 

 propagation. Still bud variation does occur. A branch of an 

 orange tree may bear lemons, or a bud of a peach tree pro- 

 duce nectarines or apricots. Buds may also be weakened by 

 association with disease organisms (as in diseased potatoes) 

 or, possil)ly, by lack of proper nutrition, and so give rise to 

 weakened stock. So we are beginning to hear of pedigree 

 selection of seed potatoes from healthy, vigorous, productive 

 hills, and of buds and scions from healthy and fruitful trees. 

 If these pomts are attended to, there seems to be no reason 

 why any variety may not by Vjud propagation be held true to 

 type indefinitely. 



All higher plants have adopted bisexual reproduction as 

 one method of jnultiplication (all seeds), and all animals 



