334 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



The contrast between sterility from physiological incompatibility and 



sterility from impotence 423 



Significance of serum incompatibilities, etc 428 



The phenomena of pollen-tube growth 436 



Types of sterility in dimorphic and trimorphic plants 440 



CONXLUSIOX 447 



BiRLIOC.RAPHY 45^ 



INTRODUCTION 



The whole subject of sterility in plants and animals has been 

 sometimes more or less obscured by a loose and fluctuating use of 

 terms. A mass of data has, however, accumulated which makes 

 possible now a more careful grouping of the facts and a more 

 exact use of terms. The su Inject may be further obscured in 

 reference to plants by the uncertainty and confusion which has 

 to some extent existed as to the terminology of sexual reproduction. 

 Here there is no dispute as to the facts either of anatomy, morphol- 

 ogy, or physiology ; thedisputehasbeenwhollyas to the applicability 

 of the terms male and female, as used by zoologists, to certain plant 

 structures that in their morphology are sporophytic. On this point 

 it will suffice to say that I shall consider pistils and stamens as male 

 and female reproductive organs during any stage of their develop- 

 ment, whether containing in the strict sense spores, gametophytes, 

 or gametes. When necessary to distinguish between them and their 

 product they will be spoken of as male and female sporophylls; 

 the embryo sac and pollen tubes (male and female gametophytes 

 with no morphological counterpart in animals) will be so desig- 

 nated, and egg cells and sperm cells will be spoken of as male 

 and female germ cells or gametes. The male and female gameto- 

 phytes are, of course, morphologically and physiologically differ- 

 entiated and constitute a new and a haploid generation. Their 

 action in fertility and sterility in higher plants is, however, closely 

 conditioned by the anatomy and the cell organization of the 

 sporophyte which produces them. 



From our i)resent knowledge of the facts and causes of sexual 

 sterility in plants, we may distinguish three main classes: 



I. Sterility from impotence, in which, as I shall use the term, 

 normal sporophylls (with spores), gametophytes, or germ cells are 

 not formed. This it seems to me is a proixr limitation of the 

 term which is, of course, fre(|ucntl\' used more generally to refer 



