POLLINATION OF VIOLA. 



795 



with the exception of the saccate appendage (spur) of the lower petal, in which the 

 nectar excreted by the appendages of the two lower stamens collects. The entrance 

 to this nectary thus situated behind the sexual organs, is only accessible through a 

 deep furrow beset with hairs, in the lower, petal; the lateral and upper petals 

 converge in front of the ovary surrounded by 

 the anthers, and over this channel in such a 

 way that the entrance is quite blocked by the 

 head of the, stigma n (in £). This head is 

 situated on a flexible style (fr in C) and is 

 hollow, and' it opens by means of a hole turned 

 towards the hairy channelon the lower petal : the 

 posterior lower margin of this opening is provided 

 with a lip-like appendage. The arithers dehisce 

 spontaneously, and the pollen collects below and 

 behind the head of the stigma, and forms a 

 yellow dust between the hairs of the channel 

 mentioned above. An insect carrying pollen 

 from another flower on its proboscis, pushes the 

 latter beneath the stigma -head, through the 

 channel and behind into the nectary in order to 

 suck the honey; by this means the foreign pollen 

 hanging to the proboscis is wiped off on to the 

 lip of the stigma -head, and it at once sticks 

 to the viscid stigmatic fluid filling the cavity 

 of the stigma -head, and subsequently sends 

 its pollen-tubes down the canal of the style. 

 Meanwhile, as the insect is sucking the nectar 

 in the spur behind, the pollen of this flower 

 lying in the canal behind the stigma- head be- 

 comes attached to the proboscis, and when the 

 latter is withdrawn this attached pollen does 

 not come in contact with the stigmatic fluid, 

 because the lip is drawn forwards by the move- 

 ment of the proboscis, and covers the opening 

 of the stigma-head from behind and below. 

 The pollen which it takes with it from this 

 flower is then wiped off in the manner already 

 indicated (by the pushing in of the proboscis) 

 on the opening of the stigma -head in another 



flower. If the insect were to insert its proboscis repeatedly into the nectary of 

 the same flower the pollen of the latter would thus come into the opening of its 

 own stigma; but insects, as Hildebrand noticed, generally do not do this (and 

 the same elsewhere) but only enter once, suck the nectar, and then visit another 

 flower. It is easy to imitate the manipulations of the insects, and to fill the stig- 

 matic cavity with pollen (from its own or another flower) by pushing a sharp thin 

 needle into the channel under the stigma-head and then withdrawing it. 



Fig. 453- — yiala tricolor. A longitudinal 

 section of flower {nat. size). B the freed ovary 

 and anthers, the former already fertilised 

 and swollen ; the filaments are ruptured and 

 the anthers carried forward by the growing- 

 ovary. C the capitate stigma with its opening 

 o and lip Ip ; gr the style (magnified). I sepal ; 

 Is appendage at base of sepal ; c petal ; cs 

 hollow spur of the lower petcd — it acts as a 

 receptacle for the nectar ; fs the appendages 

 on the two lower stamens— they project into 

 the spur and according to Hildebrand secrete 

 the nectar, a anthers ; » stigma ; v bract on 

 flower peduncle. D transverse section of 

 ovary with three placentas sp and the ovules 

 sk, E transverse section of an immature 

 anther. 



