ENALUS ACOROIDES. 
289 
is ripe and bursts (PI. XXIV., A, fig. 15) the testa also breaks 
off around the hypocotyl and remains only as a ragged easily- 
loosened cap on the top of the cotyledon (PI. XXIV., A, fig. 
17.) Thus this plant can scarcely be considered to have any 
seeds , because it is the young embryos which are dispersed at 
the opening of the fruit (PL XXIV., A, fig. 16, 18). Enalus 
acoroides is thus a new example of a “ viviparous” plant. 
These embryos are rather highly developed, as is generally 
the case in the Hydrocharitaceæ. Fig. 20 (PI. XXIV., A) 
shows an embryo with the testa a little before the bursting 
of the fruit. The cotyledon is very large and covers the 
young plumule, with its many young well-developed leaves, 
like a sheath. The hypocotyl is also large and contains much 
starch, just like the cotyledon. At the end may be seen the 
young primary root, which probably never functions, but at 
the side under the plumule a secondary root is seen pushing 
out at the base. 
The young embryos are rather heavy. They soon sink 
down into the mud, where they at once begin to grow out. 
Some embryos cultivated by myself in Jaffna after about a 
week already showed several leaves more than 1 cm. in 
length (PI. XXIV., A fig. 19). 
Enalus acoroides thus belongs to that group of plants 
where the young embryos or spores develop directly without 
any period of rest. Goebel especially has shown that this 
phenomenon is not rare in plants growing in wet localities, 
and that the well-known “ vivipary ” in the Rhizophoraceæ 
and other mangrove plants may be in some respects regarded 
as a special case of this rather common general phenomenon. 
Another example is Crinum asiaticum, where the embryo, 
however, is provided with a well-developed endosperm but 
no testa owing to the lack of integuments. Another similar 
case is Cryptocoryne ciliata, where the embryo leaves the 
cotyledon behind and only the well-developed plumule is 
detached, after having reached a high degree of develop¬ 
ment in connection with the mother plant. 
