ENALUS ACOEOIDES. 
279 
In the placentæ of Enalus it is noteworthy that the starch 
is rather more abundant at a more advanced stage than at an 
earlier one. After treatment with iodine-zinc-chloride at 
an older stage a transverse section of a young fruit shows 
a dark blue line following the walls of the fruit-cavities, 
especially in the placentæ. This is the starch-filled cells 
below the mucilage-layer (PL XXIV, A, fig. 22 sL). At an 
earlier stage there is also a considerable quan tity of starch in 
the other tissues of the ovary, but not so much and especially 
not so strictly localized as at a later stage. That the starch 
is more abundant at a later stage, when the secretion of 
mucilage rather begins to cease, may be explained by 
considering it either as a secretion formed in connection 
with the formation of mucilage and stored in the more 
superficial cells, or as stored because at a later stage it is no 
longer consumed for the mucilage formation. At all events 
the starch here seems to be of the common type which is 
stained blue, not brownish-red, by iodine. 
The result of this formation of mucilage from the walls is 
that the young ovules are quite covered by mucilage, whereas 
at a more advanced stage there is much less mucilage, and 
at the bursting of the fruit the valves are quite free from it 
upon their inner surfaces. 
No mucilage is developed from the testa as in so many 
other of the Hydrocharitaceæ. According to the description 
of the Hydrocharitaceæ by Ascherson and Gurke (5) the 
formation of mucilage in their fruits is exclusively caused 
by the mucilaginous testae. They say (5, p. 245) : “ Die 
Höhlung der Frucht ist in der Regel mit einer Gallertmasse 
angefüllt, welche meist zum grössten Teile der verschleimten 
Aussenzellschicht der Samenschale ihren Ursprung ver¬ 
dankt. 5 ’ That this is not the case in Enalus I have already 
shown above, and according to Raunkiær (22, p. 137) the muci¬ 
lage is also formed from the placentæ in Elodea canadensis. 
Concerning the importance of the mucilage for the plant 
Goebel (10) has pointed out that the penetrability for 
