CLEISTOGAMY 



55 



Lamium amplexicaule develops cleistogamous flowers twice a year, i.e. in 

 spring, before the chasmogamous forms appear, and in autumn, when the weather has 

 become cooler. Here again the pollen-grains in the closed flowers send out their 

 pollen-tubes to the stigma, either after escaping from dehisced anthers or while still 

 in anthers that remain closed; in the latter case the pollen-tubes break through 

 the anther-wall. In this case also good fruits are developed. 



According to Hildebrand {' Geschlechterverteilung,' p. 77), many flowers pollinate 

 and fertilize themselves cleistogamously under water, in cases where this is so deep 

 that the flowers cannot reach the surface. This occurs, e. g., in Ranunculus aquatilis 

 (Axell), Alisma natans, lUecebrum verticillatum, Subularia aquatica (Axell), and others. 

 Hansgirg (Bot. CentralbL, Cassel, xlv, 1891, 

 PP- 74. 75) distinguishes such flowers as pseudo- 

 cleistogamous, as contrasted with genuinely cleisto- 

 gamous ones. They completely agree with normal 

 open flowers as regards size, form, position, &c., 

 and like them possess all the specializations that 

 serve for attracting insects. 



In certain circumstances therefore the otherwise 

 normally opening chasmogamous flowers remain 

 closed, and fertilize themselves. This may be 

 brought about : i. In consequence of deficiency 

 of light, — photo- cleistogamous flowers (/); 2. in 

 consequence of high water-level, or strong current, 

 owing to which the flowers remain closed under 

 water, — hydro-ckistogamous flowers {K) ; 3. in con- 

 sequence of insufficient warmth, — thermo-ckistogamous flowers (/). 



Hansgirg (op. cit.) gives a list of all the pseudo-cleistogamous flowers known to 

 him, viz. : — 



Ranunculaceae : Ranunculus aquatilis (K). 



Nymphaeaceae : Nymphaea coerulea, N. zanzibariensis, N. madagascariensis 

 (/> or sometimes h\ Victoria regia (ditto), Euryale ferox (ditto). 



Portulacaceae : Montia fontana (/> or sometimes /). 



Caryophyllaceae ; Stellaria media and var. pallida (S. Boraeana), S. cerastoides, 

 Spergularia rubra ; Spergula pentandra, arvensis, vernalis, salina, marginata ; Malachium 

 aquaticum, Holosteum umbellatum, Cerastium arvense, Moenchia erecta; Sagina 

 Linnaei, decandra and var. micrantha, apetala (all p or sometimes /); lilecebrum 

 verticillatum (h). 



Oxalidaceae: Oxalis stricta, corniculata, Lasiandra, incarnata, lobata, Deppii 

 (all p or sometimes /). 



Cruciferae : Subularia aquatica (K). 



Droseraceae : Drosera rotundifolia, intermedia (/> or sometimes /). 



Compositae : Taraxicum officinale (/ or sometimes /). 



Scrophulariaceae : Veronica hederaefolia, serpyllifolia, agrestis, triphyllos (;> or 

 sometimes /). 



Primulaceae : Hottonia inflata {K). 



Acanthaceae : Dicliptera assurgens (/). 



Fig. 8. Cleistogamous Autumn Flower 

 of Lamium amplexicaule L. (after Hilde. 

 brand) : a, external view ; b. cut through 

 longitudinally. 



