Volume 3
A report on the progress of vegetable physiology during the year 1837 ... / Translated from the German by William Francis.
- Franz Meyen
- Date:
- 1839
Licence: Public Domain Mark
Credit: A report on the progress of vegetable physiology during the year 1837 ... / Translated from the German by William Francis. Source: Wellcome Collection.
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![4] period, while in others it takes place many months afterwards. The red colour is generally produced by the perforations of insects and by the development of Entophyta, where the leaf merely suffers an interruption in its normal development, but which is not accompanied with death. M. Mohl, on the other hand, points to a resemblance which appears to exist between the production of the red colour in leaves and that in fruits; this might perhaps be compared with the process of ripening of the juicy envelope of fruits. M. Mohl supposes that the formation of red colour in fruits is independent of nutrition, as fruits even ripen when separated from the plant in an immature state: much however might be adduced against the adoption of this view, and I cannot concur in it. In leaves, it is the cold, observes M. Mohl, which interrupts their vegetative process, and causes, when light acts on the leaves, red colour to be formed in them. In pericarps, the de- velopment of which is a more complicated process, it is the warmth which favours the perfect development, and thus hastens the last period of life. As the result of these observa- tions it may be admitted that the formation of colours accom- panies various interruptions of the normal process of vegeta- tion of the leaves and of their elaboration of the crude sap; on the other hand it must be considered as merely accidental that it occurs in those cases in organs near death, since it hap- pens, as I have stated above, frequently in leaves which con- tinue to live for some time and again become green. If leaves which have become red in winter be examined, we find the chlorophylle little or not at all changed, but perceive together with this a red colour in the cells, which, for the most part, is situated in the cells of the epidermis. I have however frequently observed red-coloured cellular sap con- taining green-coloured globules, even in the green cortical layer. Itis more seldom that red cellular sap is developed only in the outer layers of the diachyma of leaves ; in this case also, says M. Mohl, it is found in leaves which recommence their vegetation in spring more confined to the outer cells, as in Chelidonium majus, Hedera Helix, &c., while in leaves which die off in spring the formation of colour affects nearly all the cells of the diachyma, as in Jsatis tinctoria.](https://iiif.wellcomecollection.org/image/b33490065_0003_0055.jp2/full/800%2C/0/default.jpg)
