234 THE FLOWER. 



bodj-, and alternating with these five two-cleft glands, the ver- 

 tical chink or groove of which is glutinous. To each gland is 

 firmly attached, by a caudicle or stalk, a pollen-mass of an ad- 

 jacent anther. (Fig. 522.) A slight force upraising the gland 

 detaches it from the stigma and drags the pair of suspended 

 pollen-masses out of their cells. Insects visiting the blossom < 

 commonly dislodge them, the gland adhering to their legs or 

 tongues when these happen to be drawn through the adhesive 

 chink, and convey them from one flower to another. Without 

 such aid the flowers of Asclepias rarely set seed. 1 



423. Dimorphism, i. e. the case of two kinds of blossoms, both 

 hermaphrodite, on the same species, is another adaptation to 

 intercrossing. Not all dimorphism, however, lor in r/,'i.sf</>f/,i<is 

 dimorphism (4:5-1) the intent to self-fertili/e is evident. There 

 may also be dimorphism as to the perianth, not partictilarlv 

 affecting fertilization. One kind, however, and the commonest, 

 is a special adaptation to intercrossing, viz. : 



li'l. Hetcrogonous Dimorphism. (11:5. note.) This term is 

 applied to the case in which a species produces two kind> ol 

 hermaphrodite flowers, occupying different individuals, the llowero 

 essentially similar except in the andm-cinm and gynu-cium. l.iu 

 Ihese reciprocally different in length or height, and the adapta 

 lions such that, by the agency of insects, the pollen from the 

 stamens of the one sort reciprocally fertilizes the stigma of tin- 

 other. 2 This dimorphism has been detected ill about fort v genera 

 belonging to fourteen or fifteen natural orders, widely scattered 

 through the vegetable kingdom ; but there are far more examples 

 among the Rubiaceas than in any other order. Sometimes all 

 the species of a genus are heterogonous, as in Honstonia. and 



The reported sensitiveness of the gland, referred to in the first issue of 

 this volume (1S7!>), was founded upon misinterpreted observations. 



1 This peculiar ;irrangoment has been long known in a few plants, such 

 as Primula veris. 1'. grandiflora. and Houstonia. In Torrey and Grav's 

 Flora of North America, ii. :',8. :V.t ( ls|:!). these (lowers are said to IK- diu-cio- 

 dimorphous, not denoting that they an- at all unisexual, hut that the two 

 forms occupy different individuals. Their meaning was detected by C. 



Darwin, and made known in his paper "On the Two Forms or Di rphiu 



Condition in the Species of Primula, and on their Kemarkable Sexual IMa- 

 tions." published in the Journal of the Limiean Society, vi. (IS(L'), 77: repub- 

 lislied, in 1S77. as tin- leading chapter of his volume entitled "The Different 

 Forms of Flowers on Plants of the Same Species." Mr. Darwin had termed 

 these flowers simply fti',,i,ir/,lii,- ; but in this volume he adopted Ililde- 

 brand's name of //, t, ,;,*//,,/ for this kind of blossom. The difference, 

 however, affects the audnivium, and even the pollen, as well as the style; 

 when-fore we proposed for it the name of //</< rm/iiiiiiiix or /fiUror/unc dimor- 

 phism, as mentioned in a former note, 413. 



