INFLTTENCE OF POLLBM". 127 



and closely allied plant have reached the stigma, causing 

 a sufficient responsiTe action to insure fertile seed ? Pol- 

 lination does not necessarily extend to fertilization, and 

 the presence of pollen on the stigma may result in pollen 

 tubes, which, upon reaching the oTule, fail to fertilize it, 

 owing to the want of sufficient natural affinity between 

 the two. In plants like the Strawberry, the pistillate 

 varieties are merely abnormal productions, the result of 

 some chance suppression of the stamens, and in such 

 instances we may always expect an occasional develop- 

 ment of the suppressed organs. It has been said that 

 " necessity knows no law," and there are good reasons 

 for expecting that nature will make the effort, and she is 

 often successful in supplying an absent organ, as well as 

 employing various means to accomplish the same results. 

 My own experience leads me to doubt the production 

 of fertile seeds where there is a total, absence of pollen, 

 either in dioecious or other highly- developed plants, but 

 • it may not be always necessary that the pollen should 

 be supplied by plants of the same or very closely allied 

 species. For instance, for many years I had growing in 

 my grounds a pistillate specimen of the Box Elder or 

 Ash-leaved Maple {Negundo aceroides). There being 

 no staminate or male tree in my own grounds or in the 

 neighborhood, at least not within a radius of six or eight 

 miles, consequently a fertile seed on the said tree could 

 not be found. Every year for a decade this tree was 

 loaded with its unfertile seed, which were scattered 

 broadcast under the branches of some large pines — a 

 favorable position for germination if there had been a 

 perfect seed produced among the vast number. There 

 were many other species and varieties of the Maple in 

 my grounds, but none growing very near or that bloomed 

 at the same time as the Negundo. In the spring of 1879 

 I planted a large Eed Maple {Acer ruhrum), about sixty 

 feet from the Negundo, and the transplanting delayed its 



