THE MALE GAMETOPHYTE 181 



cytoplasmic streaming in the tube. Part of the evidence for motility of 

 the sperms is the frequent fusiform or vermiform shape of the gametes 

 — shapes that suggest the sperms of lower vascular taxa. The generative 

 cell also, when in the tube, has been described as moving "actively 

 and independently." Elongate and vermiform shape of the male-cell 

 nuclei is not, in itself, evidence of motility; nuclei of this type are fre- 

 quent in elongate cells of many tissues. The older view, generally 

 maintained, was that the gametes are carried by cytoplasmic stream- 

 ing in the pollen tube. Movement of the gametes along the pollen tube 

 where two-way movement in the cytoplasm occurs has been considered 

 further evidence of independent movement of the gametes and proof 

 that these cells are not carried simply by streaming of the cytoplasm 

 as the tube rapidly elongates. Changes in turgor of the tube have also 

 been considered the major cause of passage of the gametes or genera- 

 tive cell along the tube. 



Terminology of the Male Gametophyte. Since the later part of the 

 nineteenth century, there have been many changes in the terms applied 

 to the various structures and stages in the development of the male 

 gametophyte. Attempts to homologize the pollen grain with the an- 

 theridium of lower groups have been, in some measure, responsible for 

 the choice of terms. Changes in terminology have also come about by 

 the demonstration, with new techniques, that some stages described as 

 represented by "nuclei" are definite cells, with delimited cytoplasmic 

 sheaths. Tube nucleus and vegetative nucleus — long used for the nucleus 

 of the vegetative cell — are satisfactory and useful terms. They will 

 continue in use, even though, as generally believed, the tube nucleus 

 probably does not control the development of the pollen tube. The 

 vegetative cell is a naked cell, lying within the microspore wall. The 

 pollen tube is an extension of part of the inner layer of the spore wall; 

 it does not constitute "the male gametophyte," even though it may en- 

 close most of the male gametophyte. The generative cell was early 

 called the spermotogcnous cell, a term as good, or better, than genera- 

 tive cell, which is now used in the broader treatments. Both of these 

 terms have been supplanted by anfhcridial cell in many ti^eatments 

 since 1912. The term antheridial cell brings confusion to the descrip- 

 tion of the male gametophyte, unless it is used as a part of a compara- 

 tive study of the antheridium throughout vascular plants. The term 

 generative nuclei, as applied to the nuclei of the male gametes, is un- 

 fortunate, because it suggests nuclei of the generative cell. The nuclei 

 formed at division of the generative cell are the nuclei of the male 

 gametes. They have been called male nuclei, generative nuclei, and 

 spewiatogcnous nuclei, all good, in a descriptive sense, for the nuclei 

 of the gametes themselves. But it has commonly been assumed these 



