136 MORPHOLOGY OF ANGIOSPERMS 



any time in the tube up to its completed growth. The variable 

 relation of the time of this division to the great groups may be 

 illustrated by the following record : 



Among Monocotyledons the generative nucleus divides in 

 the pollen-grain in Potamogeton (Wiegand 45 ), Alisma (Schaff- 

 ner 28 ), Sagittaria (Sehaffner 31 ), A vena (Cannon 46 ), Triti- 

 cum and other grasses (Golinski 21 ), Lemna (Caldwell 42 ), and 

 Lilium (Chamberlain 32 ); and in the pollen- tube in Symplo- 

 carpus (Duggar 47 ), Tradescantia (Coulter and Rose 14 ), Eich- 

 Jiornia (Smith 39 ), Lilium (Chamberlain 32 ), Convallaria 

 (Weigand 45 ), Erythronium (Schaffner 55 ), and the Orchids 

 (Guignard 9 ). In examining this record it might be concluded 

 that the early division of the generative cell within the pollen- 

 grain is a more primitive character in general than the later 

 division in the pollen-tube. Even if this should prove to be 

 true for the Monocotyledons, it can hardly be claimed for the 

 Dicotyledons, as the following record shows: 



Among Dicotyledons the generative nucleus or cell divider 

 in the pollen-grain in Rhopalocnemis (Lotsy 51 ), Pa-paver, 

 Hesperis, Archangelica, and Mertensia (all by Strasburger 12 ), 

 Nicotiana Tabacum (Guignard 59 ), Sambucus (Halsted 17 ), 

 and Silphium (Merrell 48 ) ; and in the pollen-tube in Pepero- 

 mia (Johnson 49 ), Salix (Chamberlain 30 ), Ranunculus (Coul- 

 ter 37 ), Lathyrus (Strasburger 12 ), Euphorbia (Miss Lyon 40 ), 

 Staphylea (Strasburger 12 ), Acer (Mottier 22 ), Vinca, Nemo- 

 phila, Digitalis, and Torenia (all by Strasburger 12 ), Campa- 

 nula (Barnes 13 ), and Datura laevis (Guignard 59 ). It is 

 evident that the two conditions are found among Dicotyledons 

 in both primitive and high groups, and even in the same family 

 (as Solanaceae), and that neither one has any claim to be 

 regarded as an essentially primitive character. 



The male nuclei, formed by the division of a generative nu- 

 cleus, are possibly always associated with cytoplasm in such 

 a way that definite male cells are organized. The nucleus is 

 often the only conspicuous feature, and in every case it finally 

 constitutes the bulk of the male cell. In fact, in most of the 

 plants studied only the male nucleus has been demonstrated in 

 the pollen-tube and embryo-sac. In the following citations 

 " male nucleus " and " male cell " are used to indicate whether 

 cytoplasm was demonstrated or not. Various forms of male 



