The principles of biology . ofgrowth in these several species, they will be seen to explainthese changes in the alleged. Even more conclusive are the nearly-allied transformations occur-ring in artificially-produced varieties of the same may be named ia illustration, j In Fig. 247 is repre- •sentedone of the ordinary forms, which shows us bilateralaess ofshape along with a mode of growth that renders the conditionsaUke on the two sides while difierent above and below. Butin G. ereda, Fig. 248, wehave the flower assuming anupright attitude, and at thesame time assuming
The principles of biology . ofgrowth in these several species, they will be seen to explainthese changes in the alleged. Even more conclusive are the nearly-allied transformations occur-ring in artificially-produced varieties of the same may be named ia illustration, j In Fig. 247 is repre- •sentedone of the ordinary forms, which shows us bilateralaess ofshape along with a mode of growth that renders the conditionsaUke on the two sides while difierent above and below. Butin G. ereda, Fig. 248, wehave the flower assuming anupright attitude, and at thesame time assuming the radialtype. This is not to be inter-preted as a production of ra-dial symmetry out of bilateral symmetry, under the action ofthe appropriate conditions. It is rather to be taken as a caseof what is termed peloria —a reversion to the primitiveradial type, from which the bilateral modification had beenderived. The significant inference to be drawn from it is,that this primitive radial type had an upright attitude; and. 152 MORPHOLOGICAL DEVELOPMENT. that the derivation of a bilateral type from it, occurred alongwith the assumption of an inclined attitude. We come now to a group of cases above referred to, mwhich radial symmetry continues to co-exist with that con-stant lateral attitude ordinarily accompanied by the two-sidedform. Two examples will suffice : one a very large flower,the Hollyhock, and the other a very small flower, the Agri-mony. Why does the radial form here remain unchanged ?and how does its,continuance consist with the alleged generallaw? Until quite recently I have been unable to find any pro-bable answers to these questions. When the difficulty firstpresented itself, I could think of no other possible cause forthe anomaly, than that the parts of the Hollyhock-flower,imfolding spirally as they do, might have different degrees ofspiral twist in different flowers, and might thus not be imfoldedin sufficiently-constant positions. But this seemed a veryques
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectbiology, bookyear1864
