THE EFFECTS OF STRAINS ON STRUCTURES. 127 



point where the backward curvature takes place which gives 

 strength to the corolla-tube. This latter is also greatly 

 supported by the tube of the calyx, which, as stated, has a 

 curiously thickened cylinder within the mesophyl. 



Finally, if we may admit the existence of this adaptability 

 to strains and other external forces, and that the various 

 structures of flowers will grow in response to them and 

 develop themselves accordingly, we have a clue to the 

 interpretation of every one of the most diverse forms which 

 may be found in flowers adapted to insect agency. 



Similarly, with regard to several classes of cell structure 

 which are now recognized as having a supportive function, such 

 as collenchyma, sclerenchyma, wood fibres, etc., I would con- 

 tend that such are not formed originally and anteriorly to the 

 requirements of the plant; but that strains have been responded 

 to, and the tissues formed accordingly. Then, subsequently, 

 hereditary influences have come into play, so that noiv they may 

 appear even before there is any actual necessity for them. 



I find that M. J. Baranetzki's observations * on the thick- 

 ening of cell-walls tend to corroborate this view ; for he, too, 

 has arrived at the conclusion that the secondary formations 

 on the interior of the cell-ivalls are always in adaptation to 

 protect the cell- wall against the pressures exercised upon it. 



In alluding to the above instances of levers and mecha- 

 nical powei'S in plants, one mentally recalls how abundant 

 they are in the distribution of the bones and muscles in 

 vertebrates. These latter are, of course, situated only and 

 exactly where they are required. I cannot help thinking, 

 therefore, that the old view was fundamentally correct; that 

 such have been gradually brought into existence by the 

 efforts to meet the strains put upon them. If this be true, 

 then one and the same law has prevailed in the evolution of 

 organs in both the animal and vegetable kingdoms. 

 * Ann. des Sci. Nat. (Bat.), iv. (1886) p. 135. 



