GINKGOALES 



[CH. 



stomata, irregularly scattered over tlie lower epidermis, consist 

 of two guard-cells surrounded by 4—6 accessory cells which pro- 

 ject towards the centre of the stoma as blunt cuticularised papillae^ 

 (fig. 636, C). The epidermal cell-walls are slightly undulated 

 The distinctive form of Ginkgo leaves renders almost neghgible 

 the danger of confusion with those of other Gymnosperms; but 

 impressions of certain Fern fronds, e.g. Urdsaya reniformis Dry., 

 Pterozonium (Gymnogramme) reniforme Mart., Trichomanes reni- 

 forme Forst., and Scolopendrium nigripes Hook, might be mistaken 

 for imperfectly preserved specimens of Ginlcgo. 



Ginkgo is dioecious. The male flowers occur in loose catkins 

 (fig. 631, B) borne on short shoots in the axil' of a scale-leaf: each 

 microsporophyll consists of a short, slender, filament with a small 

 terminal scale or knob bearing as a rule 2 but not infrequently 

 3 or 4 elhptical microsporangia (fig. 631, A, A'). The microspores 

 recall those of Cycads. Jefirey* has recently called attention to 

 the occurrence of ' wings ' on the microspores of Ginkgo : these are 

 very shghtly developed and hardly warrant the use of the term 

 wing ; they present the appearance of very small shoulders giving 

 the spores a form similar to that of a brachiopod shell. The same 

 author expresses the view that Gfinkgo presents striking resem- 

 blances to the Abietineae. It has recently been pointed out that 

 the microsporangia have a hypodermal layer of cells with thick- 

 ening bands comparable with the fibrous layer in the anthers of 

 Angiosperms*. Jeffrey and Torrey^ claim that certain anatomical 

 features in the microsporangia of Ginkgo indicate a closer afiinity 

 to the Abietineae than to any .other section of the Gymnosperms. 

 The vascular bundles of the microsporophylls end in transfusion- 

 tissue which passes almost imperceptibly into the mechanical 

 elements of the sporangial wall : a similar distribution of mechanical 

 tissue occurs in Abietineous microsporangia and there is the same 

 intimate relationship as in Ginkgo between the tracheary and 

 mechanical tissues. The female flower consists of a compara- 

 tively long peduncle borne in the axil of a fohage-leaf, with two 



1 Strasburger (66) figs. 139—142; Sprecher (07) figs. 79—81. 



2 Bertrand, C. E. (74) PI. iv. figs. 9, 10. 



= Jeffrey (14) PI. xxni. figs. 7, 8. ' Starr (10). 



' Jeffrey and Torrey (16). 



