1897 ] THE LIFE HISTORY OF SALIX 169 
but the pollen grains in fig. 5 could not be distinguished from 
normal ones at this stage. The pollen grains continue their 
development, the generative nucleus organizing a part of the 
surrounding cytoplasm and becoming the center of a fusiform 
cell (fg. 4). It is hardly probable that the pollen of these 
internal microsporangia plays any part in fertilization, for it is 
uniformly later in developing than the macrospores. 
Those who regard Salix as a reduced type rather than a prim- 
itive one might consider this mixture of monosporangiate and 
ambisporangiate forms as favorable testimony, but they furnish 
better evidence that even such variations as a change from dice- 
cism to moncecism or even to an ambisporangiate condition may 
appear suddenly. The orthotropous ovules and microsporangia 
inside of the ovary are also suggestive. 
SALIX AND OTHER AMENTIFER#, 
The occasional presence of more than one macrospore in 
Salix is in harmony with what is known of other Amentifere. 
A few preparations of early stages in Populus tremuloides show 
five or six cells which are elongated to three or four times the 
length of the surrounding ones, have richer contents, and appear 
to have equally good prospects of becoming macrospores. 
The early development of the macrospore agrees more nearly 
with Nawaschin’s Betula than with any other of the described 
Amentifere. 
The tracheids, which form such a marked feature in Treub’s 
Casuarina and Miss Benson’s Castanea, do not occur in Salix. 
Salix has no caecum, unless the elongated antipodal end of the 
sac can be regarded as such. Caca are so prevalent in Casua- 
rina and the British Amentifere that Miss Benson says ‘they 
may fairly be regarded as of taxonomic value.” 
The embryo sac of Salix, at the fertilization period, differs 
from those of Alnus, Corylus, Betula, Carpinus, Juglans, and 
Myrica, in that these have antipodals which may be found with 
some ease, in some of them the antipodals being quite persistent : 
and — thick « cellulose + walls. i am — to ent that 
