488 PHANEROGAMS. 



In several families of Monocotyledons and Dicotyledons more or less con- 

 siderable deviations^ occur from the course of development of the pollen and 

 from its final structure which has been here described. Naias and Zostera deviate 

 only to this extent, that no thickening of the wall of the mother-cells takes place, 

 and that the pollen-cells themselves are very thin-walled, acquiring in Zostera a very 

 strange appearance from assuming, instead of the ordinary rounded form, that of 

 long thin tubes lying parallel to one another in the anther. The deviations are more 

 considerable in the formation of compound pollen-grains. The origin of these is 

 either that only the four daughter-cells (pollen-cells) of one mother-cell remain 

 more or less closely united, like the pollen-tetrahedra (four-fold grains) of some 

 Orchideae, Fourcroya, Typha, Anona, Rhododendron, &c. ; or the whole contents 

 of one primary mother-cell remains unseparated and forms a mass of pollen con- 

 sisting of eight, twelve, sixteen, thirty-two, or sixty-four connected pollen-cells, as in 

 many Mimoseae and Acacieae^. In these cases the cuticle or extine is more strongly 

 developed on the outer surface of the daughter-cells lying at the circumference of 

 the mass, and covers the whole as a continuous skin ; while only thin ridges of the 

 cuticle project from this skin inwards between the separate cells. In the various 

 sections of Orchideae every gradation occurs from the ordinary separate pollen-grains 

 of Cypripedium, through the four-fold grains of Neottia, to the Ophrydese, where all 

 the pollen -grains which are formed from each primary mother-cell remain united, 

 and thus a number of pollen-masses lie in one pollen-sac ; and finally to the Pollinia 

 of the Cerorchideae, where all the pollen-grains of a pollen-sac remain united into 

 a cellular mass. In this case, as in the Asclepiadeae with only bilocular anthers, 

 where the grains of each pollen-sac are firmly united by a waxy substance, it is 

 obvious that the pollen cannot be dispersed, nor can the pollen-masses fall out spon- 

 taneously from the anthers ; but the flower is provided with very peculiar con- 

 trivances by means of which insects in search of honey extract from the pollen-sac 

 the pollinia or the masses of pollen which are glued together, and again get rid of 

 them on to the stigmas of other flowers of the same species (see Book III on Sexual 

 Reproduction). 



The Female Sexual Apparatus or GyncEceum^ of the flowers of Angiosperms 

 consists of one or more closed chambers in which the ovules are formed ; the lower, 

 hollow, swollen part of each separate seed-chamber which encloses the ovules is 

 called the Ovary ; the place or the mass of tissue from which the ovules spring 

 directly into the ovary is a Placenta. Above the ovary the seed-vessel narrows 

 into one or more thin stalk-like structures or Styles, which bear the Stigmas ; these 

 are glandular swellings or expansions of various forms which retain the pollen that 

 is carried to them, and by means of the moisture which is excreted from them 

 induce the emission of the pollen-tubes. 



^ In reference to what follows compare Hofmeister, Neue Beitrage, pt. II. (Abhand. der kcinig. 

 Sachs. Gesellsch. VII); also Reichenbach, De poUinis orchidearum genesi, Leipzig 1852; and 

 Rosanoff, Ueber den Pollen der Mimosen (Jahrb. fiir wissensch. Bot. VI, p. 441). 



2 In many Mimosege the anther is, according to Rosanoff, octilocular, two pairs of small locuU 

 being formed in each anther-lobe ; the pollen-cells of each pollen-sac remain united into a mass. 



^ Compare with this Payer's view (Organogenic de la fleur, p. 725), which differs in some 

 essential points. 



