PHANEROGAMIA 



47& 



coat as in the Pea and Horse-chestnut, the plumule (i.e. the young 

 shoot) is quickly developed at the expense of the reserve materials 

 stored in the cotyledons (cf. Fig. 169; pp. 161 and 320). 



An account of the male sexual generation of the Phanerogams 

 must now be given for comparison with the above short sketch of 

 the development of the female generation. 



The MICROSPORES of the Spermaphyta are called POLLEN-GRAINS, 

 They are formed in large numbers within the MICROSPORANGIA or 

 POLLEN-SACS, which are borne singly or in numbers on the MICRO- 

 SPOROPHYLLS or STAMENS. The part of the stamen which bears the 

 pollen-sacs is usually clearly distinguishable and is called the ANTHER. 



The development of the pollen-sac (Fig. 439) commences with 

 divisions parallel to the surface taking place in cells of the hypo- 



Fiu. 437. .4, Seed of Papaver Khiirits : h, 

 the hilum ; B, seed ot'Corydalis ochro- 

 leuca ; m, micropyle ; c, carnncula : 

 C, seed of Chelidonium majus : D, seed 

 of Nymphaea alba with its arillus. 

 (After DUCHARTBE.) 



FIG. 438. A, Myristica fragrans, seed from which the 

 arillus (ar) is partly detached. B, Myristica argcntea, 

 seed after removal of the arillus ; ch, chalaza ; r, 

 raphe: h, hilum. (After WARBUIU;. } nat. si/c.) 



dermal layer ; this separates the cells of the primary archesporium 

 from an outer layer of cells. The latter give rise to three layers of 

 cells, the outermost of which is the fibrous layer, the innermost the 

 tapetum, while the intervening layer is later crushed. The arche- 

 sporium after undergoing a number of divisions forms the pollen- 

 mother-cells, each of which divides as in Pteridophytes into four 

 daughter-cells. These are the pollen -grains, and are spherical or 

 ellipsoidal in shape and provided with a cell wall ; an external 

 cutinised layer (the EXINE), and an inner cellulose layer, rich in 

 pectic substances (the INTINE), can be distinguished in the wall. 



While the male sexual cells of all archegoniate plants are depend- 

 ent on water for their conveyance to the female organs, the transport 

 of the pollen-grains to the egg-cells is brought about in Seed-plants 

 by means of the wind or by animals. However far the reduction of 

 the male prothallium has proceeded and even in the case of the 

 heterosporous Pteridophyta only a single sterile cell was present, two 



