Trelease.] 296 March 17, 



forms of trichomes do not appear to occur on the same plant, 

 though within the limits of a species both may be found on differ- 

 ent individuals. Commonly the groups of cells about the base of a 

 trichome protrude, especially on the glandular plants, so that it 

 may appear to rise from a stout multicellular papilla that is char- 

 acteristically much developed in some species which do not occur 

 in the United States. These papillae, when numerous, give a scurfy 

 appearance to the lower surface of the leaflets, especially along 

 the veins. 



The stigmas differ much in different groups, but what might be 

 taken as type-forms are connected by intermediate gradations, and 

 in related species they are so uniform as to be of little value for 

 purposes of discrimination. In most species the stigma is sagit- 

 tately dilated at the base and more or less elongated, being very 

 long in a southern form of T. purpurascens, while in T. minus, 

 etc., it approaches the deltoid form characteristic of certain other 

 European species. In T. clavatum it departs from this type, be- 

 ing short and rounded, yet decidedly oblique or lateral on the short 

 style so that it still differs essentially from the depressed-globular 

 but truly terminal stigma of Anemonella. 



Our Thalictrums show less adaptive differentiation connected 

 with their pollination than man}' genera, but they are still instruct- 

 ive. The typical flowers of Ranunculacese are of simple struct- 

 ure like those of Ranunculus, Anemone, etc., but possess petals or 

 petaloid sepals and are adapted to pollination by short-tongued 

 insects such as flies, small bees, etc. 1 Sometimes the only attrac- 

 tion for these insects is pollen, which is advertised by the coloration 

 of the floral envelopes or stamens, rarely accompanied (Anemone 

 Hepatica) by slight fragrance ; but in other instances nectar is 

 present, secreted by either of the floral organs (sepals, Paeonia ; 2 

 petals, Ranunculus, etc. ; stamens, Atragene, Pulsatilla ; pistils, 

 Caltha), and advertised similarly to the pollen. This type is mod- 

 ified in two directions ; in one reaching the complexity of Delph- 

 inium and Aconitum, which have highly specialized entomophilous 

 flowers, and in the other becoming more and more simple, finally 

 reaching a purely anemophilous state in most species of Thalic- 

 trum. 



1 For the principal literature of the subject see H. Miiller, Befruchtung der Blumen, 

 Fertilization of Flowers, and Alpenblumen: and Grant Allen, Colours of Flowers. 

 2 In which genus the external glands are to be regarded as protective. 



