Parnassia Palustris. 91 



making it impossible for them to get at the nectar. In 

 other cases, however, similar trichomatous structures, in 

 endless variety of form, merely keep off welcome and 

 invited guests from some or other part of the flower, 

 and compel them in their visits to follow some definite 

 and predetermined path. These formations, to which 

 in a preceding section I gave the name of " path- - 

 pointers," are, like the other formations, to be found 

 sometimes on the gynsecium and andrcecium, sometimes 

 on the perianth, and sometimes on the involucre or 

 other of the floral appendages. 



Among the best known of these are, perhaps, those 

 curious structures which are interposed in Parnassia 

 palustris between the anthers and petals, and are usually 

 spoken of as nectaries. In fact they are rightly thus 

 designated, for they each have two small longitudinal 

 depressions on their inner aspect, and in these nectar 

 is secreted. This nectar, however, is unapproachable 

 except on the side turned towards the ovary ; and any 

 insect that gets at it must necessarily come into 

 contact with the central part of the flower, where in 

 the first stage of flowering the pollen, and in the later 

 the mature stigma, is exposed. The insects therefore, 

 inasmuch as they must fix themselves on the centre of 

 the flower in order to suck the nectar, wUl inevitably 

 rub in some cases against the anthers, in others against 

 the stigma, and, flying from flower to flower and from 

 plant to plant, wiU. bring about allogamy. But how 



