Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . aps with those of theadjoining cells, he conceives these orifices areopened and Great variety, however,is observable in the structure of the stomata indifferent species of plants. Many plants have no stomata, either on thecuticle of the leaves, or on that of the is the case with such aquatic plants as arehabitually immersed in water. In those thatare only partially immersed, stomata are met * Fig. 22 is a magnified representation of the appearancein the cuticle of the Lyc
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . aps with those of theadjoining cells, he conceives these orifices areopened and Great variety, however,is observable in the structure of the stomata indifferent species of plants. Many plants have no stomata, either on thecuticle of the leaves, or on that of the is the case with such aquatic plants as arehabitually immersed in water. In those thatare only partially immersed, stomata are met * Fig. 22 is a magnified representation of the appearancein the cuticle of the Lycopodium denticulatum, taken in thecentral part of the lower surface of the leaf, from De 21 is a still more magnified view of the stomata in the leafof the Lilium candidtim, from Amici. t Ibid. IT. 215. VEGETABLE ORGANIZATION. 70 with in those parts exclusively which are abovethe water. The leaves of the Ranunculusaquaticus, when made to grow in the air, acquirestomata, but lose them entirely when growingunder w ater. Stomata are wanting in all plantswhose structure is wholly Botanists are far from being agreed as to theprecise functions which the stomata usual office undoubtedly is to exhalewater; but they probably also absorb air undercertain circumstances, and in particular exi-gences. The principal organs through which thefluids that serve for nourishment are receivedinto the system of plants, are those situated atthe extremities of the roots, where they aretermed, from their peculiar texture, spongioles* * Fig. 23 exhibits the termination of a root of a willow in aspongiole ; the arrangement of the cells composing which isshewn in Fig. 24, from De Candolle. 80 THE MECHANICAL FUNCTIONS. Of the functions of spongioles in absorbing fluidsI shall have occasion to speak when treating ofnutrition. But as the roots exercise a mechan-ical as well as a nutrient office, we should hereconsider them in the light of organs adaptedto procure to the
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