MONOCOTYLEDONOUS SEED OF ALISMA. 



415 



the ovary. This is the passage by which the pollen-tubes arrive 



at the micropyle. As the ovule turns its micropyle to the dorsal 



edge of the ovary, the 



pollen-tubes, after enter- 



ing the cavity of the ovary, 



must grow round the 



funicle. 



The seed almost com- 

 pletely fills up the cavity 

 of the ovary, and is fixed 

 in a median position at 

 the base of the cavity of 

 the ovary by a tolerably 

 long, bent funicle (/). 

 A vascular bundle enters 

 the funicle. The seed 

 is campylotropous, and 

 completely filled by the 

 embryo. As spermoderm 

 (ts) only a thin skin is 

 present, consisting of two 



FlG m __ Alisma Plantag<> . Median longitu . 



dinal section through a ripe achene-; ep, epicarp 



ll 



(epidermis) ; in, mesocarp; en, eiidocarp of the wal 

 of the fruit, c, a vascular bundle in this ; v*, the 

 end of the vascular bundle ; st, the withered style ; 

 t, the pollen-passage ; f, funiculus of the seed, with 

 its vascular bundle fv ; mp, micropyle ; ch, chalazal 

 end ; ts, the spermoderm ; hp, hypocotyl of the 

 embryo ; ./?, first leaf ; d, cotyledon ( * 28*). 



clearly distinguishable 

 layers of cells. Between 

 the two we see here and 

 there also a third crushed 

 layer, which comes out 



more clearly after swelling in potash. The inner cell layer of 

 cells of the spermoderm is strongly thickened on the inner 

 side. The micropyle (mp) is very prominent on the seed. The 

 radicle of the embryo lies directly against the inner side of 

 this. The radicle is somewhat swollen, and projects nipple-like 

 in the middle. If the section has cut the embryo quite medianly, 

 we see that this nipple-like projection is formed of two layers of 

 root-cap, which at the edges pass over into the epidermis. At 

 mid-height of the seed is to be seen upon the embryo an outward- 

 turned narrow notch, in which lies the growing apex of the stem 

 (plumule). This growing apex is surrounded by the cotyledonary 

 sheath. Upon the apex arises a rudimentary leaf (see figure, 

 towards the left hand) in the middle line of the outer side, which 

 completely fills up the notch. The part found between this 

 growing apex and the end of the root is the. hypocotyl. It is 



