450 BOTANICAL GAZETTE [DECEMBER 
such ideas had to be abandoned when Miss Margaret Benson reported chal- 
azogamy in Alnus, Corylus, Betula, and Carpinus. Later, Nawaschin 
announced that in /ug/ans regia the pollen tube takes an intercellular course 
within the ovule and agrees in a general way with the first reports of chal- 
azogamy. Since Miss Benson's publication it was supposed that this pecu- 
liar condition was confined to the Casuarinacez, Betulacez, and Juglandacee, 
until, in Nawaschin’s laboratory, the genera Urtica, Cannabis, Humulus, and 
Morus were found to have the pollen tube evading the micropyle and taking 
an intercellular course within the ovule, though not agreeing in details with 
the previous accounts of chalazogamy. 
New evidence is now furnished by Nawaschin,* the plants studied being 
Ulmus pedunculata and U. montana. The writer indulges in a discussion of 
the nature and location of the influence which directs the growth of the pol- 
len tube of the porogams. This influence may be entirely within the tube ; 
or within a secretion produced by certain cells of the style and nucellus which 
attract and nourish the tube; or these cells of the style and nucellus may 
serve only as mechanical guides, while the real impulse to growth rests within 
the tube. It is now probable, however, that a combination of all these factors 
constitutes the directing influence. Such might furnish an explanation for the 
porogams but not for the chalazogams. 
The behavior of the pollen tube of the elms is divided into three cate- 
gories. The first is given as the normal behavior, in which the pollen tube 
passes down the funiculus of the anatropous ovule, which is suspended from 
the top of the carpel cavity. From the funiculus the tube passes across above 
the short outer integument and through the inner one, reaching the top of the 
‘nucellus, after which the regular behavior is observed. In the second cate- 
gory the tube may branch profusely and with no definiténess within the funic- 
ulus and the integument. This branching may occur out of the tissues after 
the pollen tube has reached the tip of the nucellus. In such cases the male 
cells within the tube always follow the newest branch. In the third category 
the tube grows down the funiculus near to the bases of the integuments, then 
rows up through the inner integument to a region on a level with the nucel- 
lus tip, when it turns across to the bottom of the micropyle as before. Or, 
instead of passing up between the cells of the inner integument, it may pass 
through the chalaza into the embryo sac as the tube of a true chalazogam. 
In no case was any tissue found which could be considered especially con- 
ductive or nutritive tissue. Nawaschin thinks these two species represent a 
region in which these tissues are not yet definitely differentiated, but that the 
chalazogamic habit is being dropped as is evidenced by the varied attempts 
of the pollen tube to reach the tip of the nucellus, and by occasional reversion 
*4 NAWASCHIN, SERGIUs : Ueber das Verhalten des Pollenschlauches bei der Ulme- 
Bull. d. Acad. Imper. d. Sci. d. St. Petersbourg 8 : 345. 1898. 
