. Botany of the living plant. Botany; Plants. MODIFICATIONS OF FORM 219. a minute apical spur between them. In Lathyrus aphaca it is the stipules which become large foliar expansions, while the lamina itself is linear (Fig. 148). In such cases, which might be multiplied in- definitely, extra development of one part is accom- panied by the correlative reduction of another, as compared with normal examples. But there is no exact numerical ratio that can be put upon the proportions. They suggest in general terms, rather than with any exactness, that the excessive expenditure from the total amount
. Botany of the living plant. Botany; Plants. MODIFICATIONS OF FORM 219. a minute apical spur between them. In Lathyrus aphaca it is the stipules which become large foliar expansions, while the lamina itself is linear (Fig. 148). In such cases, which might be multiplied in- definitely, extra development of one part is accom- panied by the correlative reduction of another, as compared with normal examples. But there is no exact numerical ratio that can be put upon the proportions. They suggest in general terms, rather than with any exactness, that the excessive expenditure from the total amount of available material on one part leaves a deficiency for others. There is no doubt that this principle of correlation has a very wide application in determining the adult proportions of parts in plants. Correlation is neither a cause nor an explanation of adaptabilitv, which remains a Lathyrus Aphaca. s, stem; r . «, stipules ; b, leaf-tendril. quite independent problem. It is important (i size.) (After strasbm-ger.) to see clearly what is meant when the word "adaptation" is used. It has been used by some biologists to indicate those special modifica- tions of the plant which arise in relation to the environment. In another view all plant structures are to be regarded as the expression of the specific hereditary substance during growth and development under a certain set of conditions. The structures so developed may, or may not, be adaptations. Other things being equal, those structures which are advantageous to the plant will tend to be perpetuated by the process of natural selection. Thus although many modifications in plant structure appear to be closely adapted to the environment it is not necessary to say that they actually arose in relation to that environment. The advantage which certain features confer upon the plants that show them often appears obvious enough. But it should be realised that their recognition as adaptations is no more than an assumption :
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