CEYPTOGAMIC ANTHEEIDIA. 



233 



folds with pores may alternate with others without pores ; or finally, 

 the pores and folds may be separate. 



The form of the pollen-grains is much altered by the application 

 of moisture. Thus, in fig. 401, 1, the pollen-grain df Lythrum Sali- 

 caria, when, dry, has an ellipsoidal form, but when swollen by the' 

 application of water it assumes a globular form (fig. 401, 2). This 

 change of form is due to endosmose, and depends on the fovilla being 

 denser than the water. If the grains are retained in water the dis- 

 tension becomes so great as to rupture the extine irregularly if it is' 

 homogeneous, or to cause projections and final rupture at the folds or 

 pores when they exist. The intine, from its distensibility, is not so 

 liable to rupture, and it is often forced through the ruptured extine, 

 or through the pores, in the form of small sac-like projections (figs. 

 396, 401, 2). This efi'ect is produced more fully by adding a Httle 

 nitric acid to the water. The internal membrane ultimately gives 

 way, and allows the granular fovilla to escape (fig. 391 /). If the 

 fluid is applied only to one side of the pollen-grain, as when the pollen 

 is applied to the pistil, the distension goes on more slowly, and the 

 intine is prolonged outwards like a hernia, and forms an elongated 

 tube called a pollen-tube (fig. 397). This tube, at its base, is often 

 covered by the ruptured extine, and probably also by some of the 

 coverings mentioned by Fritzsche as intervening between it and the 

 intine. It contains in its interior fovilla-granules, and its functions 

 will be particularly noticed under fertilisation. The number of poUen- 

 tubes which may be produced depends on the num- 

 ber of pores. In some poUinia the number of 

 tubes which are found is enormous. Thus, Amiei 

 calculates that the two pollen-masses of Orchis 

 Morio may give out 120,000 tubes. 



In Okyptogamic Plants there are organs 

 equivalent to stamens, and denominated antheridia. 

 They consist of closed sacs of different forms, 

 rounded, ovate, oblong, clavate, flask-like, etc., 

 developed in diff'erent parts of the plants, con- 

 taining a number of corpuscles immersed in a 

 mucilaginous fluid, which at a certain period of 

 growth are discharged through an opening at the 

 surface. Sometimes the antheridium is a simple 

 cell, at other times it is composed of a number of 

 cells, as in Hypnum triquetrum (fig. 402, 1). An- ^ ^^^ 



theridia are sometimes confined to particular parts 

 of the plant, at other times they are more generally diff'used. Their 



Fig. 402. 1, Antheridium, a, of a moss called Hypnum triquetrum, at the monient when 

 its apex is rupturing to discharge the contents, /. 2, Pour utricles of the contents contain- 

 ing each a spermatozoid or moving corpuscle rolled up in a circular mamier. 3, Single 

 spermatozoid separated. 



