framework to the cells, that as the latter lose water, the walls tend to curve in the 

 opposite sense, and thus exert a tension on the dehiscence-line. Anthers in which 

 this mechanism is imperfect or immature do not dehisce. The pollen is normally 

 exposed passively on the recurved wall-portions. 



Germination of Pollen : Supplied with fluid and sugar in solution, as on the 

 stigmatic region of the flower, pollen-tubs are projected from one or more pores, 

 these extending as delicate processes, much in the manner of root-hairs, becoming 

 parasitic on the tissue of the style. The deposition of pollen-grains on the stigmatic 

 surface constitutes the act of Pollination : germination to a new individual normally 

 follows. Noti that the pollen-grain is a simple ' asexual ' unit ; it germinates directly 

 without reference to any other cell-unit (i.e. it is not ' male '). 



Pollinating Agents. The oldest agency for the translocation of pollen is that 

 of the wind (Anemophily). Pollination by Insect-agency (Entomophily) implies 

 correlation with animal organism, restricting the wastage of the former process. 

 Insects of lower grade (flies) may take pollen as food ; bees collect pollen for larvae, 

 taking sweet secretion of nectary-glands for themselves : Lepidoptera take ' honey ' 

 only, as also do Humming-birds : precision of visitation, speed in working, increase 

 chances of cross-fertilization and further economize pollen-output, as expression of 

 higher organization. In all cases autogamy, the transfer of pollen produced by the 

 same flower or the same individual, is to be avoided, and much floral mechanism is 

 devoted to this end. Persistent autogamy implies deterioration of the mechanism and 

 decadence, with ultimate stage in cleistogamy, in which case the flowers fail to open. 

 The ' opening ' and presentation of a floral mechanism implies that a chance is given 

 to cross-pollination with its consequences in the production of cross-fertilized seeds. 



Mechanism of Presentation. Pollen is exposed to the influence of the wind, 

 or put in the way of insect-visitors by the filaments, as expressed in : 



(i) intercalary extension, (2) growth-curvatures as effects of geotropic response, 

 (3) special movements of divergence or erection, collectively or individually, (4) often 

 correlated with a reversed action after the presentation period. 



The dehiscence of the anthers may also bear a special relation to the growth- 

 period of other floral organs; e.g., when the anthers dehisce before the stigma is 

 receptive the mechanism is proterandrous ; the converse condition being protogyny, 

 as tending to eliminate autogamy. 



Staminate flowers produce functional stamens only, the gynoecium being reduced 

 and functionless, vestigial, or wholly wanting. The same applies to the androecium 

 of ' carpellary flowers '. Staminate flowers are only ' male ' to the extent that the 

 pollen-grains germinate to give only male individuals in the life-cycle. Germination 

 of the pollen-grain commonly begins before the grains are shed from the anthers ; 

 in which case two nuclei may be distinguished in the cytoplasm. 



Microscopic Examination. 



Large stamens of Fritillaria imperialis show generalized construction. Cut in 

 transv. sect ; anthers 3 mm. broad, 4-locular, with walls of loculi of banded cells 

 2-3 deep; aqueous epidermis with finely granulated cuticle, 75/11 diam. ; hypodermal 

 banded cells, 150 /* deep, with protoplasmic contents and nuclei, the wall with 

 reticulated thickening strands. In these large ill-differentiated anthers the banded 

 cells extend over walls and connective region. Pollen-grains, oval, 50 /x, may show 

 2 nuclei. 



Buds, half-grown, of Helleborus foelidus (10 mm. diam.) with numerous enclosed 

 young anthers, are cut in transv. sect, of whole upper region, and sections of anthers 

 \\\ mm. broad) sorted out. 



Anthers 4-locular; dehiscence-layer at junction of 2 loculi on either side; 

 V.B. in connective ; pollen 30 /x ; wall differentiated only along the cavity of the 

 pollen-sacs : 



iij Epidermis of aqueous cells (40 ft) with finely granulated cuticle. 

 2) A single hypodermal layer of banded cells, 40 p deep, each with 2-3 thick 



bars (3 ft) and thickened inner wall, lignified in older stages. 

 (3) Remains of tapetum lining the cavity, and slight expression of other paren- 



chymatous layers of wall. 



For Meiotic phenomena cf. buds ofLilium Martagon : Chromosome number 24, 

 showing 12 bivalent chromosomes in the equatorial plate of the reduction spindle. 



6 



