586 THE POPULAR SCIENCE MONTHLY 



bark, or rock. Their structure is dorsi-ventral. When these little 

 plants first start, they are erect and cylindrical; the divisions of the 

 fertilized egg-cell from which they spring are at right angles to the 

 source of light. Presently, however, these little cylinders tip over 

 and, the light still coming from above, they spread out at right angles 

 to it. Thus the erect cylindrical form and radial structure soon give 

 place to prostrate leafy form and dorsi-ventral structure. It is now 

 known in at least one case, and suspected in many others, that if the 

 little plants can continue to receive light symmetrically, their form 

 will be correspondingly symmetrical. By slowly revolving them for 

 months after sowing, so that they were equally illuminated on all sides 

 in succession, I have obtained plants which were as cylindrical at the 

 end of my experiment as in the early weeks. Where the illumination 

 was equal, the structure was perfectly radial ; where it was unequal, the 

 structure was dorsi-ventral. 



This matter of bodily form, different or like in two succeeding 

 generations, depends upon the direction from which the light comes. 

 If the offspring have a one-sided illumination, as their parents did, 

 their form will be flat and- prostrate like their parents; but if the off- 

 spring are symmetrically lighted, they will be S3rm.metrically formed 

 in spite of the difference from their parents. 



So far as these experiments contribute at all to the solution of 

 biological or sociological problems they do so by indicating that like 

 influences produce like effects on the same substance, and that, al- 

 though the substance may be the same, unlike influences will produce 

 unlike results. They make us a little more confident that the child 

 of vicious parents, if itself sound, can be made into a much more de- 

 sirable citizen if brought under influences different and better than 

 those surrounding and exerted by its parents. 



The formative influences so far discussed produce normal and 

 healthy effects. The deformative and pathogenic influences which 

 affect human and other animal bodies have their parallels among 

 plants. Besides the plainly marked plant-diseases due to such obvious 

 parasites as borers, rusts, rots and mildews, there are influences no less 

 real, although easily overlooked. 



City life is unfavorable to plants. Atmospheric and soil condi- 

 tions are either bad or not bad, they are never good. One need only 

 pass along a street in which the gas-pipes have been exposed to know 

 that the soil is more or less saturated with stale illuminating gas. 

 The odor is offensive. Trees rooted in soil poisoned by large or small, 

 but always continuous doses, of illuminating gas, do not thrive. Their 

 leaves are never the full rich green of trees in the country, the foliage 

 yellows early and many leaves fall. Add leaky electric wires, leaky 

 sewers, and the putrefactions going on in fouled soil, and one realizes 

 the cause of the chronic lack of vigor of street shade trees. 



