PIANEROGAMIA : FLOWERS. 355 



extending to the entire expansion of the outer wall of the anther, some- 

 times scarcely to half of it, on each side of the longitudinal furrow. 

 Sometimes this spiral-fibrous layer extends under the epidermis, over 

 the anterior surface of the connective (as in Pachysandra procumbens), 

 or over the posterior surface (as in Hyoscyamus orientalis\ or over 

 both (as in Gentiana lutea and Erythrcea). Sometimes such a layer 

 lines each loculus on all sides (as in Strelitzia farinosa and Hippuris 

 vulgaris), either leaving the septum free or actually forming it ; some- 

 times a layer extends round each pair of loculi lying on one side, with 

 an unaltered septum (as in Calathea flavescens), or making a curve in 

 it, without entirely metamorphosing it (as in Costus speciosus]. Finally, 

 in very rare cases, all the cellular tissue, even up to the vascular bundle of 

 the connective, is converted into spiral-fibrous tissue. This multiformity, 

 left unnoticed by Purkinje*, shows the manifest inapplicability of the 

 terms proposed by him exothecium for the epidermis, endothecium for the 

 spiral-fibrous layer. The walls of the small loculi of Cycas revoluta are 

 formed entirely of a thick porous cellular tissue. In the Composite the 

 connective is formed of elegant porous cells, as are the generality of the 

 crest-dike appendages of the anthers (e. g. in the Centaurece). 



The formation of the pollen takes place in the following manner : 

 in the interior of each rudimentary loculus a process of develop- 

 ment commences within a soft row of cells, through which, in the 

 common form of the anther, a cylindrical string of cells, more or 

 less in number, the parent-cells, are gradually formed. In each 

 parent-cell the granular mucilaginous contents divide, simultane- 

 ously with the appearance of a cytoblast, into four portions, which 

 quickly become clothed by four cellular membranes ; or it may be 

 that originally two such cells are formed, and within these again 

 other two in each. These cells enclosed within the parent-cells 

 are special parent-cells. Then, by means of the secretion of a 

 gelatinous layer over the internal surface, these parent-cells and 

 special parent-cells become very much thickened, and a simple cell 

 (the pollen-cell) is produced simultaneously in each special parent- 

 cell. This, in all plants except those flowering under water, se- 

 cretes upon its outer surface one or more layers, forming the exter- 

 nal pollen membrane, which assume, in some fcases, peculiar and 

 remarkable forms. During this last perfecting of the pollen, the 

 parent-cells and the special parent-cells are dissolved and absorbed. 

 In many Monocotyledons, especially Liliacece, the product of the so- 

 lution of the parent-cells is a clear or dark yellow 7 fluid, of gluti- 

 nous or oleaginous (?) nature, which adheres to the external pollen 

 membrane. In the Onagracece, in the parent-cells or special parent- 

 cells (as in the Equisetacea), a spiral thickening layer is formed, 

 which is not dissolved with them, but adheres in long threads to 

 the perfect pollen granules. A part of the product of the solu- 

 tion of these cells is frequently viscid, and glues the four pollen 

 granules belonging to one parent- cell firmly together (pollen quater- 

 narium) ; sometimes it unites only two (in Podostemon), and some- 

 times a greater number of granules, (in some Acacias, for instance, 



* De Cellulis Antherarum Fibrosis. Breslau. 

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