1354 A TEXTBOOK OF THEORETICAL BOTANY 



leaf-axils, cleistogenes are formed among the normal spikelets of the inflores- 

 cence, usually in its terminal portion, and their numbers are inversely 

 correlated to the amount of soil moisture available, in other words cleisto- 

 gamy is ecologically conditioned. Leersia oryzoides, on the other hand, is 

 almost completely cleistogamous, under all conditions. 



Fig. 1 26 1. — Triplasis purpurea. A, Base of internode showing cleisto- 

 gamous spikelet enclosed by prophyll. B, Cleistogamous spikelet. 

 C, Spikelet from terminal panicle. D, Grain from cleistogamous 

 spikelet. E, Grain from terminal panicle. {After Chase.) 



Many Orchids are cleistogamous, some species entirely so, others 

 partially. Some species normally chasmogamic have cleistogamic varieties 

 and the distinction appears to be genetic and heritable. Thus local popula- 

 tions of a species may be wholly cleistogamic, others wholly chasmogamic. 

 Cephalanthera grandiflora has its pollinia attached to the stigma by preco- 

 ciously formed pollen tubes and, left to itself, this may be enough to produce 

 some seed, though much less than if pollination be normally carried out. 



Cleistogene flowers are sometimes produced underground. Some 

 species of Comrnelina produce such flowers on the rhizomes, the seeds 

 ripening and germinating in place. A Brazilian species of Cardamine, C. 

 chenopodiifolia (Fig. 1262), bears cleistogamous flowers while still in the 

 seedling state, the axillary pedicels bending downwards and the flowers 

 developing below ground among the roots. They show typically arrested 



