i62 Pescott, Reproduction of Terrestrial Orchids. [vo[''^xxxiv 



The Genus Pterostylis. 



Taking this genus as a type, and especially as the Green- 

 hoods are so well known, the methods of reproduction and 

 increase may be explained at length. 



The method of the continuance each year of what may hv. 

 called the parent plant is well known. When the vegetative 

 growth appears from the tuber and pushes its way to the 

 surface to grow the foliage, stem, and flower, it is enabled to 

 do so by the plant food that was stored in the tuber by the 

 work of the foliage of the previous year. As this store of food 

 is slowly exhausted, the tuber gradually shrinks and shrivels 

 until a mere skin remains. While growth is taking place, 

 however, a small root is pushed out from the stem, just above 

 the old tuber. From this quickly grows a new tuber, in which 

 the growing foliage stores another food suppl}-. When the 

 flowering has been completed the plant slowly dies, leaving 

 only a new tuber in the soil, the old one having disappeared 

 and the skin having rotted away. 



Regarding the increase in the tuber system, or the produc- 

 tion of juvenile tubers, the genus naturally separates into 

 three groups. 



Group I.— When the tuber breaks into vegetative growth, 

 and, after the foliage has appeared above ground, the root 

 system is formed. This root system comes from the main 

 stem which proceeds above from the tul)er, and ne\er from the 

 tuber itself. Several roots Ijranch out laterally and almost 

 horizontally through the soil. Usuall}' they are very close 

 to the surface. Apparently a liberal air supply is needed for 

 the roots and for the subsequent development. As the lateral 

 filamentous root system is developing, the tip of each root 

 begins to swell, the swelling increasing week by week until each 

 strong root has terminally developed a new tuber. Later 

 the roots die, leaving several new tubers in the soil, and quite 

 awav from the parent tuber. 



In the reproduction of the parent tuber, the new season's 

 tuber is always found slightly below — sometimes only one- 

 eighth of an inch — the older tuber. This ulterior position is 

 necessary, so that the laterally produced or juvenile tubers may 

 gradually reach a lower and more suitable strata of soil. Thus 

 one plant, in addition to reproducing the parent tuber, may 

 grow two or three, or even more, juvenile tubers, thus con- 

 siderably increasing the species. 



Frequently the filamentous roots, which finally terminate 

 in the juvenile tuber, are several inches in length. Plcrostylis 

 mUani> often produces these roots to a length of six or eiglit 



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