26 THE PLANT. 



applied by the flowers first fertilised for their own de- 

 velopement. It is a fact, that many plants will not 

 repay the trouble of cultivation, if the climatic condi- 

 tions are not sufficiently favourable to effect the 

 thorough ripening of all the flowers, but serve only to 

 ripen part of them. 



With oats it often happens that in warm moist 

 weather side-branches will spring from the axils of the 

 leaves, when the principal culm is already shooting 

 into ear ; whence it happens, that at the end of the 

 period of vegetation the plant is found to bear both 

 ripe and unripe seeds. 



The condition of the soil, as to porosity or compact- 

 ness, influences the radication of plants. The fine fila- 

 ments of the root, which are often coated with cork-like 

 matter, are lengthened by the formation of new cells at 

 their extremities, and they are obliged to exert a certain 

 pressure, to force their way through the particles of 

 earth. 



The root-fibrils will always extend in that direction 

 in which they encounter the least resistance ; and this 

 lengthening necessarily presupposes that the pressure 

 wherewith the new-formed cells push aside the particles 

 of earth, must be somewhat greater than the cohesion 

 of the particles. The strength with which the root- 

 fibres force their way through the soil, is not equally 

 great in all plants. Those plants which have roots 

 formed of very fine fibres are but imperfectly developed 

 in stiff, heavy soils, wherein other plants with thicker 

 and stiffer root-fibres will grow luxuriantly. The very 

 resistance which the heavy soil opposes to the spreading 

 of the roots of such plants tends to strengthen their 

 fibres. 



Of the cereals, wheat, with a comparatively feeble 

 ramification of roots in the upper layers of the soil, still 

 forms the strongest roots, which often penetrate several 

 feet down into the subsoil ; for a certain degree of com- 

 pactness in the surface soil is favourable to the devel- 

 opement of its roots. There are instances on record, 

 where parts of a wheat-field had been trampled down 



