AArciOSPERMS. 



403 



given in the appendix. In many cases the long series of far-reaching changes set up 



by fertilisation extends to parts, which do not belong to the ovary or even to other 



parts of the flower; and since these parts belong physiologically to the fruit and are 



usually combined with it to form a 



single whole which is distinctly 



separate from the other parts of the 



plant, a structure of the kind, the fig 



(Fig. 335), the strawberry and the 



mulberry, for example, may be termed 



a pseiidocarp. 



At a certain time either the fruit 

 with its seed becomes detached from 

 the plant, or the seed separates by 

 itself from the opened fruit; this is 

 the time of maturity. In many species 

 the whole plant dies down when it 

 has ripened its fruit ; such a species 

 is termed nwnocarpic, as bearing fruit 

 only once ; monocarpic plants may 

 be distinguished into those which bear 

 fruit in the first period of vegetation 

 {annual plants), or not till the second 

 {biennial pla7its), ox lastly not till several 

 or many vegetative periods have passed 

 [monocarpic perenttial 'p\z.\'\i'S,, as Agave 

 americana). Most Angiosperms how- 

 ever are polycarpic, that is the vitality of the plant is not exhausted by ripening 

 its fruit, but the plant continues to grow and fructify periodically, and \'i polycaipic 

 percntiial. 



Anatomy of the flower. Of the structural details of the flower which have been 

 already described two will be again noticed here, the conducting tissue and the nec- 

 taries, our knowledge of which has been increased by the labours of various investigators 

 in quite recent times. 



Conducting tissue'^. The tubes which the pollen-grains develope on the \iscid surface 

 of the stigma have often a considerable distance to travel in order to reach the ovules. 

 The conducting tissue has a double duty to perform ; first to supply the pollen-tubes 

 with plastic material for their growth, for they soon exhaust the food-material stored up 

 in the pollen-grain, and secondly to assist the tubes to find their way to the micropyle 

 and to enter it. For this purpose a conducting tissue is necessary in the style first and 

 afterwards in the ovary or on the ovule itself. This tissue is formed in plants whose 

 style has no canal by conversion into mucilage of the outer layers of the walls of the 

 cells in the tissue which occupies the place of the canal, and which is thus converted 

 into conducting tissue ; in plants which have a canal, the cells that line it show a 

 similar secretion to that on the papillae of the stigma. It is only occasionally, for 



Fig. 334. Fonnationof adventitious embryos in i'^K«/6/Vz<>i'rt/<r /the 

 cells at the apex of the nucellus filled with cell-contents; beneatli it the 

 oospore with two nuclei and the remains of one of the synergidae. // 

 several adventitious embryos have formed in the cells of the nucellus ; the 

 nucellus is displaced, and strongly thickened cells of the integument are in 

 contact with the embryo-sac. The oospore is present and has divided 

 into three cells. denotes the oospore, i- a synergid. ae the adventitious 

 embryos, J the cells of the integument. After Strasburgcr. Magn. 

 about 150 times. 



• Behrens, Ueber d. anat. Bau d. Griffels u. d. Narbe (Dissert. Gottingen, 1875).— Capus, Anat. 

 du tissu conducteur (Ann. d. sc. nat. Bot. 6. ser. T. VII, 1878).— Dalmer, Ueber d. Leitung d. Tollen- 

 schlauche bei d. Angiospermen (Jen. f. Zeit^chr. Naturw. Bd. XIV).— [Strasburs^cr, Neuc Unters. ii. 

 <\. Befruchtungsvorg;. b. d. Phanerog. 1S85. .See also note on page ,^06.] 



n d 2 



