BOTANY. 



lottction 

 polleu. 



course of each day. In such floors as require their 

 policy, hairs are usually placed in such a situation at 

 the entrance of the flower, as not only to exclude 

 wet, but also to compel all insects that enter it to 

 pass over the stamens. The intervention of insects 

 is singularly displayed in the Arix/oloc/iia clrmatitu, 

 the flower of which always remains in an erect posi- 

 tion, and the stamens are shorter than the pistil. The 

 consequence is, that the pollen falls to the bottom of 

 the corolla ; and if insects be excluded by means of 

 thin gauze, the flower does not yield fruit. Fre- 

 quently too, as a particular insect, (Tipula jn-inii- 

 corn.x), which is sometimes wanting, performs this 

 office, the same abortive effects occur. Many parti, 

 culars are recorded of the means by which different 

 insects accomplish these ends. The sketch which 

 we have given, is sufficient to give an idea of their 

 agency. 



To protect the pollen from moisture, which it has 

 been hinted is peculiarly noxious, as it bursts the 

 grains of pollen if applied previous to the maturity 

 of the different parts of the flower, flowers fold their 

 petals, or droop when moisture prevails. The droop- 

 ing ot the flower occurs in the Gaianthn*, l.eiicojum, 

 1'riti/laria, and others. This does not appear to be 

 owing to the weight of moisture, as the fruit, though 

 much heavier, remains erect. The closing of the 

 AnagalKs is so remarkable, as to have obtained for 

 that flower the epithet of the poor man's weather 

 glass. Linnaeus remarked, that they lose this delicate 

 sensibility after the anthers have done their duty, 

 ipoiheses Such are the leading facts connected with the 

 propa- functions of the stamens and pistils. Many hypothe- 

 ses have been formed to explain their reciprocal agen- 

 cies, and the advocates of each has urged a host of 

 arguments in support of his opinion and it may fair- 

 ly be said, that each has argued with equal truth. 

 The doctrine of EpiffdHeiis, or of the mixture of the 

 fluids derived from the pollen and the stigma, seems 

 the most probable, and that which has received the 

 strongest support from experiment. Koelreuter, by fe- 

 cundatingthe female flower of onespecies of Nieotiana, 

 with the pollen of another species of the same genus, 

 produced a hybrid plant, retaining some of the cha- 

 racters of each of its parents, but resembling neither 

 of them exactly. This is a curious subject, and pro- 

 mises to reward very richly those who may feel dispo- 

 sed to prosecute such inquiries. 



We now come to the productions of the combined 

 agency of the stamens and pistils, which receives the 

 general name of fruit. All the peculiarities have been 

 detailed in the first Section of this Part, and it is im- 

 possible to add any thing beyond what is to be found 

 in TERMINOLOGY, (Part I. Sect. ii. Art. 67.) The 

 uses of the different kinds of seed vessels are obvious- 

 ly to protect the young seed until the period should 

 arrive, when it is to enter upon a new class of func- 

 tions. The colouration of fruit seems also to depend 

 on the same causes that influence the colours of leaves 

 and flowers, which have been already detailed as am- 

 ply as our limits would permit. 



The fall { the fruit does not take place, when the 

 plant is healthy, until it is fully ripe. At that pe- 

 riod the designs of nature are fulfilled ; and as it cea- 

 ses to require nourishment, by a law of vegetation 



69 



[ion 



it. 



tlir vessels gradually lose their vigotir, at last die, the Vtgetublt 

 stalks fade away, ami the fruit falls, while the branch 

 on which it flourished retains its vigour and energy 

 unimpaired. 



SKCT. VII. General Summary. 



WE have now traced the plant through all its gra- General 

 dationa, from Us embryo state to that of its complete summary, 

 formation. We have seen it gradually ascending 

 from the most imperfect rudiments, and ultimately 

 attaining a magnitude unknown among other organ- 

 ised bodies. In its most perfect state, the tree 

 consists of separate, solid parts, pervaded by regu- 

 larly organised vessels. These vessels we have found 

 are not distinct from each other, but form a conti- 

 nuous series of central and alburnous vessels, which 

 terminate in the leaf, whence other vessels, that re- 

 ceive the name of cortical vessels, turn through thr 

 bark. Each of these parts and vessels of trees, we 

 have learned, perform a series of determinate func- 

 tions. It now remains for us to view them in the re- 

 lations which they bear to each other. But before 

 we can effect this in a satisfactory manner, it is neces- 

 sary that we should ascertain, as far as possible, the 

 nature of the matter which supplies the plant with 

 nourishment ; the nature of the fluids which exist in 

 it ; whether a circulation is- carried on, and in what 

 manner ; and lastly, we shall learn the extent of our 

 knowledge respecting the various changes effected 

 by the operations that are known to go on. We 

 shall then be enabled to take as complete a view of 

 the vegetable economy as the present state of our 

 knowledge will permit ; and although such a survey 

 will rather shew the imperfection, than any real pro- 

 gress of our investigations in vegetable physics, yet it 

 may be useful, in so far as it may excite some doubts 

 in the minds of those who now believe that little re- 

 mains for the exercise of talent. Ingenious men have 

 long employed themselves in endeavouring to discover 

 the nature of the food by which plants are nourished, 

 and it is singular to observe how very little they have 

 doneintheirinquiries. And although the cause of their 

 want of success appears very obvious, as it has esca- 

 ped so many, it may not be irrelevant to make a few 

 observations respecting it. Almost every philoso- 

 pher that has engaged in physiological researches, 

 has received some previous impressions in favour of a 

 particular branch of science, and his particular views 

 on that subject, have too generally determined his 

 physiological speculations. Thus the mechanical 

 philosopher fancies, that every function of organised 

 beings is carried on by means of mechanical agents ; 

 while the chemist, on the other hand, considers such 

 means inadmissible, and refers every phenomenon to 

 the agents of his science both of them forgetting, 

 that there is a certain unknown something which we 

 call life, that maintains a marked and important cha- 

 racter in the living economy, and which must influ- 

 ence, at least the contrary cannot be proved, every 

 operation that is performed either in the animal or 

 the vegetable. A neglect of this principle has often 

 led the most illustrious ornaments of our species to 

 attempt what others more cautions, though posses- 

 sing less real genius, have shunned. 



