1889.] NATURAL SCIENCES OF PHILADELPHIA. 63 



of the season the ends of the petioles widen ; the petioles themselves 

 shorten ; and careful observations in many plants will show that the 

 final result of this process is the bud-scale. When, again, the season 

 for a renewal of growth occurs, the same process appears inverted. 

 The small scale grows larger and wider. Often a perfect petiole is 

 reached before a trace of leaf appears. In some species of Ash, and 

 in the Dwarf Horse-chestnut (Aesculus parvi flora), this transition is 

 particularly evident. The result of the examination will clearly 

 establish the fact that a bud scale is' a transformed leaf to be sure, 

 but a leaf in which the longitudinal growth has been arrested, and 

 a quickened growth secured for the base of the petiole or stipule. 

 We may more correctly say that a bud-scale is a transformed stipule, 

 or dilated petiolar base. 



Examining carefully the same growth-course in the clover or the 

 rose, there is seen the same gradual modification. The stipules are 

 enlarged until the leaf blades wholly disappear in the sepals ; the 

 petals, still the same modified stipule, widen and enlarge. No other 

 conclusion can be reached. But in the rose the sepals sometimes 

 narrow, and the leaf-blade reappears at the apex. In some varieties 

 grown in winter forcing houses, a perfect pinnate rose leaf appears. 

 This is the case, notably, with a variety known to florists as Madame 

 Ferdinand Jamain (in America " American Beauty.") Clear as it 

 is to the mind that when carefully traced, the petal of a rose is 

 formed of an enlarged stipule, and not of a fully planned leaf, the 

 positive evidence is not furnished as freely as in the case of the 

 sepal, but specimens of Rosa humilis, sent to me in 1883 by Miss 

 Jennie E. Whiteside, of Harmonsburg, Pennsylvania, give an ex- 

 cellent illustration. This form has been figured and described by 

 Mr. Sereno Watson in the Garden and Forest for February loth, 

 1889 as Rosa humilis, var triloba. The trilobed petal is simply a 

 case in which the usual stipule forming the petal of the rose, has 

 again had its normal growth accelerated towards a perfect leaf. 

 The central lobe is in fact no more than a dilated petiole, with the 

 stipule represented by the two lateral lobes, in its normal position 

 at its base. The same process from the total arrestation of petiole and 

 leaf blade to the abnormal dilation of the stipule to form the petal, 

 can be traced in magnolia, as made plain in the paper above cited. 



When we come to formulate the general proposition that the bud- 

 scales of branches, and the sepals and petals of flowers are modified 



