EeprodBcti osperms: Mic *-].,>- M.^. H 



ANDROECIUM, of Stamens, usually few, 5-10 (range i-iooo), devoted to 



the production of pollen-grains or microtpern : hence the stamen is regarded aa 

 equivalent to a leaf (microtportpkyll). with a petiole (filament), and lamina, rudimentary 

 as ' connective', bearing 4 sporangia in a pain along the margin of the lamina, as two 

 sori each of two sporangia ; a limiting case, hence remarkably constant for the vast 

 majority of flowers. Anthers with two sporangia are exceptional. 



The sporangia are termed ' pollen-sacs', and the whole set of 4 fimrtilUM the 

 anther (globed) ; a single V.B. in filament and connective supplies the anther. The 

 sporangia dehisce in pairs, by a special mechanism, and the pollen-grains are liberated 

 in the air. 



NoU theoretical names, and older more colloquial terms as equivalents. 



Development of Pollen : the young anther-lobes consist of simple paren- 

 chymatous units, and at an early stage, cells are differentiated in each lobe as an 

 Arcksfvrittm, distinguished by refractive or denser plasmatk contents with con- 

 spicuous nuclei. At first covered by only a single layer of epidermal cells, by active 

 division the archesporial units produce a central mass of ' mother-cells '; while an 

 outer tract subdivides to wall-layers, 2-3 cells thick, as the lobes of the anther enlarge. 

 The mother-cells tend to isolate, and round off, presenting remarkable phenomena in 

 nuclear division, the importance of which does not immediately appear, as : 



Meioais : In each mother-cell, after elaborate preparatory changes (to diakineais), 

 a nuclear spindle is formed ; the chromosomes are distributed in pairs over the equatorial 

 plate, but longitudinal division of each chromosome is checked. Spindle-fibres 

 attach instead to the individual chromosomes still imperfectly divided, with the 

 that half the number arc withdrawn to each pole (anaphase), there to reco 

 constitute the daughter nuclei (telophase), each with only half the regulation 

 since whole chromosomes are sorted out and not halves. Hence termed a Redaction 

 Division '. The daughter nuclei divide again directly with a spindle-mechanism, the 

 chromosomes now completing their longitudinal fission ; but the resulting nuclei con- 

 tinue to present the half-number (hence termed * kapbid\ as diatingUJaTifd from the 

 full somatic or diploid type). The division of the mother-cells in this manner marks 

 a critical departure in the life-history, and the 4 resultant nuclei produced in each, 

 which are not necessarily at first separated by new dividing waifs, may be termed 

 a ///r<u/-group. These nuclei segregate cytoplasm, round-off, and secrete wall- 

 membranes, soon becoming isolated as the young pollen-grains. In this way pollen- 

 grains are developed in groups of four, and the tetrad-formation may persist until 

 they are mature ; in some cases they remain so associated. 



Nutrition of Pollen-grains : A zone of cells around the mass of i 

 early differentiates as a feeding-layer, with refringent contents and active 

 the manner of the epithelium lining a duct, as the Tafxhtm. Food-en} 

 secreted into the cavity of the ' pollen-sac ', and the pollen-grains grow to pack the 

 pace, being fed from without. When the latter are fully grown only a trace of the 



tapetal layer persists, with no cell-structure. Oily colouring matters derived from 



>Uow, brown, orange-red, or even brae. 



the tapetum commonly tint the pollen-grains yellow, brown, orange-red, or 

 Pollen-grains when fully formed appear as uninucleated cells, 

 30-50 /i diam. (10-100), spherical, or more or less tetrabedrally 

 reserve-contents as oil-drops and proteids, and a double wall, or ejrimt of coticnhvued 

 layers covering an intint of cellulose. Thin areas in the former, or in both layers. 

 constitute ports, often definite in number and position ; very commonly 3 at 3 angles. 

 Sculpturing of the outer wall, spinous projections, etc., may give characteristic 

 appearances to specific or generic types. Tetrad-groups may persist (JShtm). or 

 packets of more (Acacia) ; in extreme cases (Orchids) the entire contents of each 

 pollen-sac may remain united in a waxy cake-like mats as a PoUtmxmm. Exposed to 

 the air, pollen-grains dry off, becoming shrunken and folded, and are normally air- 

 borne by wind, or carried by hair)- insects: very rarely (some aquatics, Z+sitrm) 

 discharged under water. 



Dehisoenoe of Anther. Two pollen-sacs on either side open by one fine of 

 separation, in response to hydrostatic tensions in the living ceOs of the outer wall- 

 layers as these tend to lose water. Sub-epidermal layers show a thickenir 

 or reticulated strands, which may be lignified, these being so arranged as a 



5 A 2 



