242 THE FLOWER. 



increase is by cleistogamous self-fertilization, which thus offsets 

 the incidental disadvantage of the former mode. 



437. In general, the cleistogamous are like unto the ordinary 

 flowers arrested in development, some arrested in the almost 

 fully formed bud, most at an earlier stage, and in the best 

 marked cases with considerable adaptive modification. In 

 these, " their petals are rudimentary or quite aborted ; their 

 stamens are often reduced in number, with anthers of very small 

 size, containing few pollen-grains, which have remarkably thin 

 transparent coats, and generally emit their tubes while still 

 enclosed within the anther-cells ; and, lastby, the pistil is much 

 reduced in size, with the stigma in some cases hardly at all 

 developed. These flowers do not secrete nectar or emit any 

 odor : from their small size, as well as from the corolla being 

 rudimentary, they are singularly inconspicuous. Consequently, 

 insects do not visit them ; nor, if they did, could thej r find an 

 entrance. Such flowers are therefore invariably self- fertilized ; 

 yet they produce an abundance of seed. In several cases, the 

 young capsules bury themselves beneath the ground, and the 

 seeds are there matured. These flowers are developed before, 

 or after, or simultaneously with the perfect ones." l In Grasses, 

 however, as in some Dicotyledons, there is much less modifica- 

 tion and more transition. For when Leersia half protrudes its 

 panicle, in the usual way, the included half is fertile and the 

 expanded portion sterile (or almost always so), although the 

 flowers may open and exhibit well-developed anthers, ovaries, 

 and stigmas. But when similar panicles remain enclosed in the 

 leaf-sheaths, they are mostly fruitful throughout. 



438. Fully to apprehend the economy of cleistogamy in pollen- 

 saving alone, and contrariwise to estimate the expense of 

 intercrossing, one should compare the small number of pollen- 

 grains which so completely serve the purpose in a t} T pical cleis- 

 togamous flower (say 400 in Oxalis Acetosella, 250 in Irnpatiens, 

 100 in some Violets) with the several thousands of all entomo- 

 philous cross-fertilized flowers, rising to over three and a half 

 millions in the flower of a Peony, also their still greater number 

 in many anemophilous blossoms. To this loss should be added 

 the cost of a corolla and its action, also of the production of 

 odorous material and of nectar. No species is altogether cleis- 

 togamous. Thus cleistogamy, with all its special advantage, 

 testifies to the value of intercrossing. 



1 Darwin, Forms of Flowers, 310. 



