FERTILIZATION 157 



in this laboratory in Lilium philadelphicum (Fig. 36, H), L. 

 iritjrinum, and Anemone patens Nuitalliana; and at the close 

 of 1900 .Miss Sargant 46 published a resume and general discus- 

 sion of the subject. More recently, Guignard 4S has described 

 double fertilization in Zea and Xaias major; Land has discov- 

 ered it in Cnicus and possibly in Taraxacum ; while Guignard 53 

 has added Nigella damascena and Ranunculus Cymbalaria', 

 and Frye 60 has described its occurrence in Asclepias Cornuti. 

 Karsten 55 has also confirmed the occurrence of double fertili- 

 zation in Juglans, investigating several species; Shibata 54 has 

 added Monotropa uniflora, Ikeda 58 Tricyrtis hirta, Strasbur- 

 g er 59 Ceratophyllum demersum, Guignard 56 species of Nico- 

 tiana and Datura, as well as of Capsella and Lepidiumf 4 

 Wvlie 6T Elodea, and Frve ° 8 Casuarina. 



It will be seen that the phenomenon is not restricted to a 

 few groups, but is widely displayed among both Monocotyledons 

 and Dicotyledons ; among the former having been observed in 

 Xaiadaceae, Hydroeharitaceae, Gramineae, Liliaceae, Amaryl- 

 lidaceae, and Orchidaceae ; and among the latter in Juglanda- 

 ceae, Ceratophyllaceae, Ranunculaceae, Cruciferae, Resedaceae, 

 Malvaceae, Ericaceae, Asclepiadaceae, Solanaceae, and Com- 

 positae. Probably it is not safe to. infer the general occurrence 

 of double fertilization, although the observations already include 

 sixteen families, about forty genera, and over sixty specie-, 

 besides inferential testimony in other species from the form and 

 activity of both male nuclei and from the phenomenon of xenia. 

 In any event, it is common enough to demand a general explana- 

 tion of its significance, its place in the history of Angiosperms. 

 and especially whether it is really fertilization or merely triple 

 fusion. It has certainly introduced among' structures alreadv 

 difficult of interpretation a phenomenon that immensely in- 

 creases the difficulty. The subject will be discussed briefly 

 under endosperm (Chapter VIII), and only such general 

 details presented here as have been observed in connection with 

 the process. 



It is claimed by Guignard for Lilium, and confirmed by 

 Miss Thomas in Caltha, that the first male nucleus extruded 

 from the tube passes to the polar nuclei. The frequently vermi- 

 form and spiral character of this nucleus has suggested the possi- 

 bility of independent motion; but this form is by no means con- 



