214 BOTANY AND PHARMACOGNOSY. 



cellulose, and an outer, known as the " exine,'' apparently con- 

 sisting chiefly of cutin ; in some cases the exine also contains an 

 oil which is colorless, as in Salvia, or yellowish, as in lavender, 

 and in some instances it may contain a viscid substance, causing 

 the pollen grains to adhere, as in CEnothera. The grains may be 

 smooth or variously sculptured ; in most instances the exine is 

 unevenly developed, leaving thin places through which the pollen 

 tubes protrude in germination ; these give the appearance of 

 grooves when the grains are dry, and the number of grooves is 

 characteristic for different species ; in most of the Compositse 

 they are three in number ; in the Labiatse there are six, while in 

 Crocus they are wanting (Fig. 119). 



The epidermal cells of the stigma are quite characteristic. 

 The cells of the epidermis, or so-called " stigma-epithel," may be 

 palisade-like, forming a more or less wart-like mass, as in the 

 viscous stigmas of the Umbellifer?e, or the outer walls may be 

 modified to rather broad papillae, as in matricaria and arnica, 

 or they may be developed into hair-like processes, as in 

 Crocus. The pollen tubes either enter the style through an 

 open canal, as in the violets, or they penetrate into the conducting 

 tissues of the style, either through the papillae, as in Malva, or 

 through the middle lamella of two neighboring papillae, as in 

 Atropa Belladonna. 



The important tissue of the style is the conducting tissue ; in 

 styles which are hollow it forms the lining of the canal, the cells 

 resembling those of the stigma-epithel ; in styles that are solid 

 the conducting tissue occupies the central axis and consists of 

 somewhat elongated cells, the walls of which are generally thick, 

 frequently strongly refractive and possess the property of swell- 

 ing, being furthermore separated by large intercellular spaces. 

 Surrounding the conducting tissue are thin-walled parenchyma 

 cells, in which the fibrovascular bundles are distributed, the num- 

 ber of groups of the latter corresponding to the number of carpels 

 that compose the gynaecium. There may also occur secretion cells, 

 containing mucilage, as in IMalva, or oil and resin, as in matri- 

 caria. Occasionally, the parenchyma is replaced either in part 

 or entirely by mechanical cells, and the epidermal cells may be 

 modified to hairs. 



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