ANGIOSPERMS. 



40 J 



must break 



through in 



germination, and which is termed the cokorhiza or root- 



sheath ; a similar state of things is found also in Dicotyledons, in Geranium for 

 instance, where there is no appearance of a hypophysis as in Capsella, but the apex 

 of the root is bounded on the posterior side by the tissue of a many-celled suspensor. 

 It is not uncommon for lateral roots as well as the primary root, which we have 

 hitherto been considering, to be formed in the embryo before the seed is ripe, as 

 for example in many of the Gramineae and in some Dicotyledons, such as Impatiens 

 according to Hanstein and Reinke and in Cucurbita according to Sachs ; in Trapa 

 natans the primary root soon ceases to develope and lateral roots are formed from 



FIG. 332. Older embryos of Alisma Plantago \ c cotyledon, / growing point of the stem, a hypocotyl, w root, 

 h hypophysis. In VI the dermatogen is shaded. From drawings by Hanstein. 



the hypocotyledonary portion of the axis (hypocotyl}. The degree also of develop- 

 ment which the embryo reaches in the seed is very different in different seeds. In 

 some plants the plumule has several leaves besides the cotyledons while it is within the 

 seed, whereas the embryo of many Angiosperms which live as parasites or sapro- 

 phytes is an undifferentiated mass of cells with no sign of root or cotyledons. 



Adventitious embryos and poly cmbryony. Great as are the variations in the develop- 

 ment of the embryo in the cases which have now been described, they have this 

 feature in common, that the embryo proceeds from the oospore. But, according to 

 Strasburger's interesting discovery 1 , there are a number of Monocotyledons and 

 Dicotyledons in which the embryos never or seldom come from the oospore, but are 

 shoots from cells of the nucellus adjoining the embryo-sac. To the list of such plants 

 belong Funkia ovata,Nothoscordtim, Citrus Aurantium, Mangifera indica, Coelebogym 

 ilicifolia. Funkia ovata (Fig. 334) has an egg-apparatus composed as usual of two 

 synergidae and an oosphere ; the oosphere also is fertilised, but the oospore seldom 

 or never developes into an embryo. Instead of this, adventitious embryos of the kind 

 above-mentioned make their appearance after fertilisation. Cells of the nucellus 

 covering the apex of the embryo-sac (Fig. 334 /) become filled with protoplasm, 

 swell up and divide (Fig. 334 //), and as a considerable number of the cells of 

 the nucellus put out these shoots, we have here an evident case of polyembryony. 



1 Strasburger, Ueber Befruchtung u. Zelltheilung, Jena, 1878; Id., Ueber Polyembryonie (Jen. 

 Zeitschr. ftir Naturwiss. Bd. XII). 



[2] Dd 



