MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBTA UNIVERSITY 11 



The parapetalous stamens must be regarded as abnormal supernamerary parts, very 

 common in the Rosaceae and rather characteristic. Any theory as to their origin can 

 be only a matter of speculation. I have seen no explanation given. As stated above, 

 many authors have regarded the bractlets as representing the united stipules of two ad- 

 jacent sepals. This suggested to me that the parapetalous stamens might have the same 

 relation to the antipetalous stamens as the bractlets have to the sepals, only with the 

 difference that they have remained free. Their position, viz., one on each side and a 

 little outside of the antipetalous stamens, is the one to be expected of such modified 

 stipules. Acting on this suggestion, I traced the fibro-vascular bundles of those stamens 

 in Horkelia sericoleuca, Pickeringii and argyrocoma and found that they united with those of 

 the nearest antisepalous stamens (these species have parasepalous instead of parapetalous 

 stamens) before they reached the bottom of the calyx, as shown in plate 1, fig. 3, us. 

 This fact would suggest that they represent in a certain way the stipules of the antisepa- 

 lous stamens. The fact that they develop before the antisepalous stamens is also par- 

 allel to the earlier development of stipules. 



In several species of Potentilla with 30 stamens as for instance, P. recta and sid- 

 phurea (fig. 14 ), the additional series of 10 stamens (ps) have exactly the same position 

 relative to the antisepalous stamens (as) as the outer series of 10 parapetalous (pp) 

 stamens has to the antipetalous stamens ( ap). That would mean that not only the anti- 

 petalous but also the antisepalous stamens had stipules. There is, however, another 

 explanation, perhaps neither better nor worse, viz., that the antipetalous stamen and its 

 two neighboring parapetalous stamens represent a trifoliolate leaf. The Horkeliae with 

 20 stamens have apparently parasepalous instead of parapetalous stamens ( fig. 8). 



It must be remembered that the presence of supernumerary stamens is not uncom- 

 mon. Such a condition is often found in the antipetalous and antisepalous stamens, so 

 that two stamens instead of one are found opposite one or more petals or sepals. The 

 parapetalous (and parasepalous, if present) are seldom duplicated in flowers with less 

 than 30 stamens. There are very few species of Potentilla that have a greater number, 

 and in such cases it is nearly impossible to make out the arrangement. Of the North 

 American species most have about 20, some as many as 30, and one Mexican species 

 about 40 stamens. 



Many species of the tribe have fewer than 20 stamens. In such cases it is generally 

 the parapetalous series that first disappears. The number then becomes 10, as com- 

 monly in Potentilla rivalis, P. leucocarpa, P. biennis (Fig. 10) and Horkelia [Ivesia) 

 pygmaea. If further reduction occurs, which is even more common, the antipetalous 

 stamens are also lacking and the androecium is represented by the 5 antisepalous 



