240 



CRYPTOGAMS AND PHANEROGAMS. 



tion of the sporangium in the Equisetince and Lycopodince is in the 



main the same. 



In the PHANEROGAMS the Microsporangia are termed Pollen- 

 sacs. They take their origin from a large group of cells, which, in 

 the Angiosperms, lie immediately beneath the epidermal cells of the 

 anther. In the developed, but not yet mature, sporangium (pollen- 

 sac) there are to be found: (as in the Vascular Cryptogams) (1) an 

 internal group of mother-cells which give rise to the pollen-grains 



J> 



FIG. 247. Development of an anther. .4 Transverse section of a young; anther of Doroiii- 

 citm iiKU'roji/iylfmii. The formation of the 4 pollen-sacs commences by divisions of the 

 hypoderrnal cells (at m, for instance). These cells divide by periclinal walls into external 

 cells which only take part in forming the anther-wall ; and internal cells, which corres- 

 pond to the Archesporium, and from which the spores are derived. These spore-forming 

 cells are drawn with thicker walls in B-E. The commencement of the vascular bundle is 

 seen in the centre. B An older stage ; the pollen-sacs already project considerably. It 

 is the cells in the hypodermal layer which are active and in which tangential divisions par- 

 ticularly occur ; / v vascular bundle. C A corresponding longitudinal section. D Trans- 

 verse section through an older anther, the thickness of the wall outride the mother-cells 

 nf the pollen-grains is already increased, and it becomes still thicker by the division of the 

 hypodermal cells : its most external layer of cells but one, becomes transformed into the 

 " fibrous cells." E Transv r erse section of a still older pollen-sac of Menyanthes ; sm are 

 the mother-cells of the pollen-grains surrounded by the tapetnm (t), external to the tapetum 

 is the anther-wall, which is still far from being fully developed. The sub-epidermal layer 

 becomes " fibrous," and the cells lying inside it become dissolved, together with the tapetum. 



(microstores), in this case also formed in tetrads; (2) a group of 

 cells surrounding these, of which the internal ones form a tapetal 

 similar to that in the Vascular Cryptogams ; the tapetum 



