6 MEMOIRS FROM THE DEPARTMENT OP BOTANY OF COLUMBIA UNIVERSITY 



MORPHOLOGY. 



ORGANS OF VEGETATION. 



Most of the members of the tribe are perennial herbs. The perennial portion con- 

 sists generally of a short ascending rootstock, densely covered with remains of basal 

 leaves and their scarious stipules. To this is sometimes added a deep woody tap root. 

 In species growing in arid regions the rootstock is generally very thick and woody and 

 often much branched. Arctic and alpine species are generally cespitose. A few species 

 of Potentilla are annuals or biennials with a branching root. Among ours P. fruticosa 

 L. is a shrub 1-4 feet high and P. tridentata Ait. is also somewhat shrubby. 



The flowering stem is so variable that very little may be said concerning it in this 

 connection. In the alpine and arctic plants it is often subscapose. In Duchesnea and 

 some species of Potentilla, the stem is prostrate and rooting. Fragariu, Argentina 

 {Potentilla Anserina, Egedii and anserinoides) and sometimes Dwchesnea produce true 

 runners. 



The inflorescence is more or less distinctly cymose. Where the stem is very leafy 

 and the upper leaves not mucli reduced, the flowers become apparently axillary (the 

 supina and argentea) groups of Potentilla. In Duchesnea, Argentina and the Tormentilla 

 groups of Potentilla, the flowers are borne on long axillary pedicels. 



All species, so far as I know, have stipules. Those of the basal leaves are, as a rule 

 scarious and more or less brown ; those of the stem leaves, foliaceous. In Tomocarpa, 

 {Potentilla fruticosa and its relatives) they are all scarious and more or less sheathing. 



The leaves are usually described as compound. This is, however, more or less 

 erroneous, as the so-called leaflets are very rarely articulated to the rachis ; but, on the 

 contrary, often decurrent. Only a few, as for instance Slbbaldiopsis {Potentilla tridentata), 

 have truly compound leaves. In this species there is an evident joint and the leaflets 

 are tardily deciduous. As there is no name that applies to the principal divisions of a 

 leaf divided entirely to the midrib, I am obliged to use in the descriptions the word 

 leaflets for these divisions. For the secondary divisions, I shall use segments, lobes or. 

 teeth, according to the depth of the incisions. 



In Fragaria, Duchesnea, Slbbaldiopsis and Slbbaldia the leaves are ternate. In 

 Ghamaerhodos they are twice ternately divided. In Potentilla'^ they are pinnate or digi- 

 tate, with three or more leaflets. In Comarum and Horkelia (including Ivesia), they are 

 pinnate and in the sub-genus Ivesia (except H. Webberi, Baileyi and saxosa) the leaflets 

 are verv numerous, small and more or less imbricated. 



1 Here as well as for the most part in the following discussion, understood in its usual extensive limitation. 



