1900] DOUBLE FERTILIZATION IN COMPOSITAE 253 
indicate that double fertilization may be more frequent than is 
commonly supposed. 
So far as recent work indicates, the spermatophytes produce 
two male cells, The persistent appearance of a second male 
cell, seemingly as well organized as the one which functions, has 
found no better explanation than a phylogenetic one, although 
it would be hard to explain why a cell which has long been 
abandoned continues to be well organized. We may well inquire 
whether a simultaneous fertilization of the egg and of the endo 
sperm nucleus may not be universal in angiosperms. 
The study of the mature embryo-sac of Erigeron and of 
Silphium was undertaken for the purpose of determining the 
fate of the second male cell. The first named genus was chosen 
because a large number of ovules in different stages of develop- 
= could be cut at once; the second, because of the differen- 
tation shown by the disk and ray flowers. 
MATERIAL AND METHODS. 
Material was collected in the vicinity of Chicago, from June 
lg July 20, 1900, Collections were made at all hours of the 
¥,and all material was killed in the field. The outer involucral 
= Erigeron were removed and the heads closely trimmed, 
y ough of the receptacle being left to hold the ovules 
SOE A I per cent. aqueous solution of chromo-acetic 
a killing and fixing agent. Carnoy’s fluid was 
oe pe unsatisfactory. The material was passed through 
nto paraffin and cut in serial sections 3.3 # and 6.64 thick. 
that for aay of treating Silphium was slightly different from 
ing the oo The ovules, except those intended for trac- 
issueg z = the pollen tube, were freed from the surrounding 
‘emperature ated plunged into chromo-acetic acid at a 
acid me about 100°, and were allowed to remain in ge 
hey were ut two hours. After washing and dehydrating, 
soy Ep  “brough xylol into paraffin at a temperature 
: : Sec i : ° . 
Tictotome. Hons 2~5 w thick were cut on a Reichert rocking 
