GROUP V. AXGIOSPERM.E ; DICOTYLEDONES. 509 



English Iris; /. Xiphium (Xiphion vulgare) the Spanish Iris; /. reticulala 

 and persica. The rhizomatous Irises are classified, according to the pre- 

 sence or absence of hairs (beard) on the perianth-segments, into bearded 

 (e.g. Jris yermanica,florentina,etc,.') and beardless forms (e.g. Iris Pseudacorus, 

 the Yellow Flag, andfoetidissima, both of which are British). 



Fam. 3. IXIOIDE.E : the flowers, which are frequently zygomorphic, are 

 each invested by a spathe : stem, usually a corm. 



In the Gladiolece, the zygomorphism of the flower is well-marked, but the 

 flower may be either straight and erect (e.g. Tritonia, Montbretia, Spar- 

 axis), or curved (e.g. Gladiolus). Gladiolus illyricus (communis\ the lesser 

 Gladiolus or Corn-Flag occurs in England. 



CLASS X. DICOTYLEDONES. 



The ripe seed (Fig. 245) may be albuminous, containing a mass 

 of endosperm and a relatively small embryo, as in the Umbelliferae 

 and Euphorbiaceae ; but sometimes the embryo is relatively large 

 and the endosperm occupies only a small space, as in the Labiatae : 

 more commonly the seed is exalbuminous, the endosperm being 

 wholly absent, and then the embryo, which has large and fleshy 

 cotyledons, fills the entire cavity of the testa, as in the Rosaceae, 

 the Leguminosse (Fig. 320), and the Composite. Perispenn is 

 rarely present, either together with endosperm (e.g. some Piperales 

 and Nymphaeacese), or alone (Chenopodiales, Caryophyllales). 



The embryo (see p. 401) usually has distinct members, consist- 

 ing of an axis and two opposite cotyledons; in rare cases, e.g. 

 Corydalis, only one cotyledon is present, or abnormally three may 

 occur, as is occasionally the case in the Oak, the Sycamore, and 

 the Almond. In parasites and saprophytes which are devoid of 

 chlorophyll and which have very small seeds, such as Monotropa 

 and Orobanche, the embiyo is quite undifferentiated, and it con- 

 sists of only a small number of cells. 



The axis of the embryo frequently persists as the main axis of 

 the plant which grows in length and produces numerous less 

 vigorous lateral shoots; but it often happens that some of these 

 lateral branches subsequently grow as vigorously as the main axis : 

 when this is the case, and when also the lower and feebler shoots 

 die off, a head, such as is common in forest-trees, is the result ; in 

 the case of shrubs, vigorous branches are formed quite low down 

 on the main stem. The branching of the stem is almost invariably 

 axillary and lateral : it is frequently monopodial (p. 19), but in 

 many forest-trees the stem (trunk) and branches form a sympo- 



