294 PROCEEDINGS OF THE ACADEMY OF [1893. 



strate this as an actual fact as in the case of the orange, but I feel 

 sure some one may meet with an abnormal specimen which will 

 prove the point. 



The varying intensity of rhythmic waves of growth may come 

 to be regarded as a leading factor in the development of form. 

 These waves certainly have to do with the varying sexual characters 

 of trees, as I have shown in other papers. The fact brings us near to 

 a certain knowledge of the origin of form, though we have still to 

 learn what causes the variations in the intensity of these waves. 

 Even in these different forms of citrus fruits the varying forces 

 affect fertility. In the case of the Tangerine orange, in which the 

 secondary rhythm has been accelerated to such an extent as to 

 cause abortion in the whole of the lower carpellary system, the 

 seeds necessarily are not formed. In the case of the Navel, where 

 the secondary wave has only drawn part of the force from the lower, 

 it usually results in so much weakening of the latter's power that 

 few or no seeds result. The Navel is usually a seedless fruit. 



Morphology of the Stipule in Comarum palustre. 



I have claimed that when axial growth is arrested to form the 

 inflorescence, a suppression of leaf-blade, and a corresponding 

 development of stipule or dilated petiole usually occurs in the mor- 

 phological conception of a flower. In other words, instead of pet- 

 als and sepals being metamorphosed leaves, they are more critically 

 metamorphosed stipules. 



This is well illustrated in Comarum palustre. Examining a 

 branch we find only a stipule at the lowermost node. Ultimately a 

 leaf with two pairs of leaflets and one odd one. Then growth 

 becomes suppressed as the flowering stage approaches. The next 

 node has the leaf trifoliate, the next with only a single terminal 

 leaflet, the next with the stipule only. It is seen that all the next 

 nodes have stipules only and the sepals are but stipules. I have 

 before noted that Rosacea', afford the best illustration of the fact 

 that petals are but enlarged and modified stipules, and not trans- 

 formed "leaves" as generally understood. 



Fertilization of Malva rotundifolia. 



Prof. Herman Mueller, in his work on cross-fertilization of 

 flowers, indicates that Malva rotundifolia invariably fertilizes itself 

 in case insects should not visit the flower in its earliest stages. 

 Unless, as I think may be the case, flowers behave differently in 



