748 PHYSIOLOGY. 



nalis, those of the Victoria regia, of several Cactt, and of many 

 AracecE, present us with the most marked illustrations of rise of 

 temperature. 



That this evolution of heat is dependent upon the combination 

 of the oxygen of the air with the carbon of the flower, was con- 

 clusively proved by the experiments of Vrolik and Vriese ; for 

 they showed that the evolution of heat by the spadix of an Arum, 

 is much greater when it is placed in oxygen gas than in ordinary 

 atmospheric air ; and that when introduced into carbonic acid 

 or nitrogen gases, it ceased altogether. 



2 . Of the Essential Organs of Eepkoduction. — Sexuality 

 of Plants. — The stamens of flowering plants, as has been already 

 repeatedly stated, constitute the male apparatus, and the carpels 

 the female. That the influence of the pollen is necessary to the 

 formation of perfect seed may now be considered as positively 

 established in an immense majority of flowering plants ; and 

 although certain apparent exceptions occur, which we find it im- 

 possible to explain in the present state of our knowledge, where 

 perfect seeds have been produced Avithout the agency of pollen, 

 still such isolated cases must not be allowed to overthrow the 

 great mass of evidence which may be adduced to show, that some 

 pollinic influence is generally essential to the production of a 

 seed with a perfect embryo. It would appear from various ob- 

 servations, that a kind of Parthenogenesis takes place in some 

 plants, and hence, that a single impregnation is sufficient to 

 produce several generations. 



While the presence of two distinct sexes may thus be shown 

 in flowering plants, both of which are necessary for the forma- 

 tion of perfect seed ; it seems almost certain that flowerless 

 plants, in like manner, possess certain organs, which represent 

 the two sexes of flowering plants, and that their functions are 

 accordingly, essentially the same. It is quite true that the ex- 

 istence of sexuality has not been proved in all the Cryptogamia, 

 but as it exists in the greater number, we may fairly conclude 

 from analogy that it is present in all. (See Structure of the 

 Reproductive Organs of Flowerless Plants, pp. 367 — 393.) 



SEXUAL REPRODUCTION OF PLANTS. 



We have just stated, that a seed is only to be considered per- 

 fect when it contains an embryo which is capable of germinating 

 and ])roducing a new plant ; and that for its formation the 

 mutual influence of two sexes is necessary, as has been conclu- 

 sively shown in an immense majority of flowering plants, and 

 hence wc conclude from analogy that such an influence is ne- 

 cessary in all. 



In flowerless jdants, also, as noticed above, the influence of 

 two sexes has been shown to be necessary in the majority of 



