Scutellum in Zea Mats. 
121 
the structure of the latter. Xylem elements creep round its circum- 
ference in order to reach the point from which a branch is given off. 
In the upper part of its course, where branches are frequent, this leads 
to the formation of a complete girdle of xylem round the phloem of the 
bundle- trunk (Figs. 16-18). Its structure in this region is that which 
Professors Strasburger and Jeffrey call amphivasal, though near the base 
it is, as we have seen, collateral with a compact group of xylem on the 
ventral side (Fig. 15). 
The larger branches are also amphivasal as a rule (Figs. 16-18), but 
the girdle of xylem is commonly incomplete in the branchlets. The minute 
structure of two branchlets is shown in Figs. 20 and 21, both drawn from 
the same section. The xylem consists of completely lignified tracheids 
(x, Fig. 21) ; the phloem of rather long cells with dense contents and large 
nuclei, and a few much elongated elements, narrow and almost empty 
( c.c . in Figs. 20 and 21). These form a core to the branchlet. We have 
called them central cells. 
The structure of the branchlets recalls the transfusion tissue described 
in the rootlets of Stigmaria by Professor F. E. Weiss. We have adopted 
the term albuminoid cell for the thin- walled phloem elements with thick 
contents (alb., Fig. 20). They are seen in the larger branches to be the 
direct continuation of the phloem in the bundle-trunk (Figs. 16-18). 
Conclusion. 
The scutellum of Zea Ma'is is distinguished by the presence of glands 
on its dorsal face^ and by the transfusion tissue connected with its vascular 
system. Both these features are undoubtedly connected with its prolonged 
function as a sucking organ. 
We have found neither glands nor transfusion tissue in the scutellum of 
Triticum , Hordeum , or Avena , but in these grasses the endosperm is floury 
and less copious than in Zm, and it becomes semifluid so soon as ger- 
mination begins. Its reserve of food is exhausted in a few days, and 
the whole fruit is then cast off by the seedling which in future shifts for 
itself. Thus the scutellum acts as a sucking organ for a short time only, 
and it has to deal with a floury endosperm which is already half dissolved 
by the action of the water absorbed in germination. 
The endosperm of Zea , on the contrary, is mainly homy, and is absorbed 
and dissolved by degrees. Sachs’s well-known figure, which we have repro- 
duced with some modification in Fig. 1, shows that part of the endosperm 
is floury, and in this part digestion probably begins. 
It is a significant fact that the floury endosperm as shown in such 
a section is in contact with that region of the scutellum-surface in which 
glands are most frequent. Possibly their presence there indicates the 
