10 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY 



obcordate; in Fragaria, Duchesnea, Potentilla arguta, fruticosa and tridentata and their 

 allies nearly orbicular ; in Horkelia proper, cuneate-obcordate or nearly strap-shaped ; in 

 Ivesia, Sibbaldia and Ghamaerhodos spatulate or obovate, in Gomarella {Ivesla depauperata 

 and I. subidosa) narrowly linear, and in Comarum ovate and long-acuminate. 



The color is also variable ; white in Fragaria and soihe species of Potentilla and 

 HorJcelia ; yellow in Sibbaldia, most Potentillae and some Horkeliae, and dark red or purple 

 in Comarum and Comarella and some species of Potentilla. 



STAMENS. 



The most common arrangement of the stamens met mth in the tribe is twenty in 

 three series (See plate 1, fig. 9 ). The outer series consists of ten stamens, placed two 

 and two inside each petal. These are designated as parapetalous stamens (pp) by Alex- 

 ander Dickson.^ The other two series consist each of five stamens, in the one placed 

 right opposite the petals [antipetalous stamens, ap) and in the other opposite the sepals 

 {antisepalous stamens, as). In Potentilla the antisepalous stamens are generally the in- 

 nermost, a fact that seems rather strange on a casual observation. The contrary would 

 rather be expected. One would rather expect that the different series would follow 

 each other in the following order: bractlets, sepals, petals, antisepalous stamens, anti- 

 petalous stamens and the different series of pistils. This is also the order in the Horkeliae 

 with 10 stamens. In the Horkeliae with twenty stamens [Ivesia) the antipetalous sta- 

 mens are also the innermost, as they should be (fig. 8.) Why should not the same be the 

 case in Potentilla f A further investigation shows that the antisepalous stamens, as a 

 rule, are the largest and the antipetalous the smallest. By examining the opening buds 

 it is easily seen, that the order in which the stamens develop is as follows ; first the anti- 

 sepalous, then the parapetalous, and lastly the antipetalous stamens, i. e., the inner, outer 

 and middle most commonly in Potentilla, the middle, outer and inner in Horkelia (in- 

 eluding Ivesia ). The conclusion is that the antisepalous stamens, being the older, must 

 really belong to a series outside that of the antipetalous ones. Their place inside 

 must be explained in the following way : In Potentilla the staminiferous disk is always 

 more developed at the points where the petals are attached, making the disk more or 

 less pentagonal in outline. The expansion of the disk at the five corners has naturally 

 carried the antipetalous stamens farther out so that they are in the same periphery as 

 the antisepalous stamens or even are carried beyond the same. In Horkelia where the 

 disk is obsolete and has about the same development all around, the antipetalous and 

 antisepalous stamens remain in their proper relation. 



' Seemann, Journal of Botany, 4 : 275. 



