[Vol. 2 



346 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



prets this as a vegetative fusion in support of his interpreta- 

 tion of vegetative fusion in the ascus. Karsten ('08) de- 

 scribes the divisions of the zygote nucleus into four nuclei in 

 Spirogyra jugalis, but does not state the relation of the nuclei 

 to the germling (second division sometimes omitted). Tron- 

 dle ('07) interprets the process in Spirogyra Spreeiana as 

 presenting but a single division of the zygote nucleus. Re- 

 sults of this nature, so divergent from expectations based on 

 the normal history in many other organisms in widely sepa- 

 rated groups, are usually received with considerable reserve, 

 particularly where they are pioneer investigations in a group 

 not yet studied. Recently Kurssanow ('11) in a thorough 

 study of nuclear division and germination of the zygote in 

 two species of Zygnema (Z. cruciatum and Z. stellinum) has 

 shown that the process is normal, there being two successive 

 divisions, three of the nuclei usually degenerating, while one 

 becomes the nucleus for the single germling characteristic of 

 the Zygnemaceae. Occasionally only two of t lie nuclei de- 

 generated, but then two germlings were formed, an interest- 

 ing case showing a tendency to retain what is believed to 

 be the ancestral condition where four germlings are formed 

 as in the Mesotaeniaceae, while in the desmids two germlings 

 are regularly formed. 



Other cases cited as examples of vegetative nuclear fusion 

 and classed with nuclear fusion in the ascus, are those of the 

 endosperm nucleus with the second sperm nucleus in seed 

 plants (Harper, 'Of)), and (Fraser, '13) nuclear fusions in 

 paraphyses and in hairs of the excipulum of certain discomy- 

 cetes. Such cases, however, cannot be legitimately compared 

 to fusion in the ascus, since those nuclei are shut off from 

 further participation in the line of successive ontogenies. 



The example cited by Harper of Boveri's ('88) experiment 

 in shaking sea urchin's eggs after fertilization, resulting in 

 the production of an abnormally large larva with 72 instead 

 of 36 chromosomes, is in a different class from most of the 

 other examples of vegetative fusion given. This is equiva- 

 lent to a true double fertilization and it is quite within the 

 bounds of possibility that among many such larvae some 



