190 Structural and Physiological Botany. Ne 
According to Hofmeister, the embryonic vesicles are cells of proto- 
™ 34 fe : i . ve m J | Pe ws et vas ad 
ee > 
P it 
plasm destitute of a cell-wall lying below the apex of the embryo-sac, 
which is sometimes more, sometimes less strongly thickened, it having 
- there a much greater refractive power of light and often a wax-like gloss. 
According to Schacht this shining mass, called by him the filiform 
apparatus, is usually striated, and forms an essential part of the 
Fic. 364.—Separated em- 
bryo-sac of Helotro- 
pium, the endosperm 
consisting of a long row 
of cells ; one of the cells 
in the middle has already 
divided transversely; p 
pollen-tube ; & rudiment 
of the embryo. 
Fic. 365. — Longitudinal 
section through a seed 
of Nymphea: c testa; 
6 perisperm; a@ _ endo- 
sperm ; embryo. 
embryonic vesicles, destined to conduct the fer- 
tilising substance from the pollen-tube to the 
balls of protoplasm, subsequently perishing, 
while the embryo continues to develope. 
The radicular end of the embryo is 
always developed first on the suspensor, 
and hence the radicle of the mature em- 
bryo is almost always turned towards the 
micropyle. During its growth the em- 
bryo is almost always, except in Orchidese, 
nourished by a tissue developed in the 
embryo-sac (Fig. 364), and termed the 
albumen or endosperm, which is absorbed 
in 1ts immediate neighbourhood by the 
growth of the embryo. If it is entirely 
consumed in this manner, the mature seed 
is exalbuminous ; 1f a portion of it is left, 
it is albuminous. | When a portion still 
remains of the tissue of the nucleus itself, 
this is called the pertsperm. Cannacez 
have a perisperm, but no endosperm, 
while Nymphezaceze (Fig. 365) have 
both. The cells of these tissues” are 
finally filled with a quantity of nutrient 
substances of all kinds, which serve for 
the nutrition of the young plant when 
germinating. Rees § 
These processes exhibit an alternation of 
generations, although obscure. 
corresponds to the microspore, the embryo-sac to the macrospore, of 
_ the heterosporous Vascular Cryptogams (see Chap. VI., p. 245). 
The pollen-grain— 
