ai6 



MORPHOLOGY OF MEMBERS. 



clothed with the remains of the leaves, or are naked, as in Tree-Ferns, procumbent 

 species of Aspidium, Palms, species of Aloe, &c. 



If a comparison is made between the amount of development in bulk which 

 takes place in the leaves and in the axis of a shoot, we find , as extremes on one 

 side, for example, the Cacti {Cereus, Mammillaria, Echinocadus, &c.) with gigantic 

 axes and entirely abortive leaves, on the other side the Crassulaceae with fleshy 

 crowded leaves and comparatively weak stems; or on one side the underground 

 tubers of the Potato with scarcely visible scales, and on the other side the bulbs 

 of Liliacese with fleshy scales which entirely envelope the short stem. 



In reference to the formation of leaves M'hich appear on the shoots, it must 

 first be noted whether the same axis always produces only similar leaves or such 

 as gradually vary in form. The first is the case, for example, in most Muscineae, 

 Ferns, Lycopodiacese, Rhizocarps, all Equisetaceae, and most Conifers ; the latter, 

 on the other hand, occurs commonly in shrubby Dicotyledons. In Monocotyledons 

 and Dicotyledons (to a certain extent even in Conifers) it not unfrequently happens 



Fig. 156.— Rhizome of Pteris aquilina; /, //, /// the underground creeping axes; jj the apex of one of them ; 1—6 the 

 basal parts of the leaf-stalks ; 7 a young leaf; b a decayed leaf-stalk, the basal portion of which is still living and bears a bud 

 Ilia; the hairy threads are roots which arise behind the growing apex of the stem. 



that the different forms of leaves are distributed over different generations of shoots ; 

 certain shoots produce, for example, little or nothing but foliage-leaves, others 

 produce only bracts with or without flowers {e. g. Begonia). In such cases the 

 shoots may be designated, according to their leaves, scaly shoots, leafy shoots, 

 bract-axes, flowers, peduncles, &c. On this point further details will be given in 

 Book 11. 



It is of very common occurrence with Cryptogams and Angiosperms (not 

 with Gymnosperms) for a persistent primary axis or branch-system to continue to 

 grow underground, and to send up only at intervals long foliage-leaves or shoots, 

 which subsequently disappear in their turn and are replaced by others. When 

 such axes or branch-systems lie horizontally or obliquely in the ground, and 

 produce lateral roots, they are called rhizomes (Fig. 156), (as in Iris, Polygonatum, 

 Pteris aquilina and many other Ferns). Frequently they die at the posterior and 

 continue to grow at the anterior end. Underground tubers and bulbs are more 

 transitory structures, usually lasting only for one period of vegetation ; the former 



