J NGIOSPEKMS. — MONO CO TYL EDO. VS. 



443 



formed retains the thickness which it had already reached in tlie bud near the apex of 

 the stem. But in Dracaena., Aloe and Yucca of the LiHaceae a further growth in 

 thickness begins subsequently at a considerable distance from the apex of the stem, and 

 may continue even for hundreds of years and be the cause of considerable though 

 slow increase in the diameter of the stem. But the process is very different from 

 that in Conifers and Dicotyledons. A layer of the fundamental tissue parallel to 

 the surface of the stem is changed into a meristem which continually produces new 

 closed vascular bundles and between them parenchymatous permanent tissue ; in this 

 way a more or less evidently stratified net-work of slender anastomosing bundles 

 is produced, the arrangement and connection of which are easy to recognise in stems in 

 which the parenchyma between the bundles has perished from exposure to the weather. 

 This compact net-work of closed bundles forms a kind of secondary wood which 

 surrounds in the form of a hollow cylinder the space in which the original common 

 bundles of the stem run isolated and loosely compacted as long threads. This 

 mass of new thickening tissue in the arborescent Monocotyledons resembles the 

 secondary wood of the Conifers and Dicotyledons in belonging entirely to the stem, and 

 in having no genetic connection with the leaves, in which latter respect it differs 

 from the original common bundles. Exceptions to the course of the vascular bundles 

 as briefly described above occur in different Monocotyledons. Slight modifications 

 arise by the bundles forming in their course oblique or transverse connecting branches 

 (anastomoses), as in the tuberous stems of the Aroideae, the elongated internodes 

 of the stems of many of the Cyperaceae, and in some other instances ; or they may unite 

 with bundles from lower leaves before they reach the periphery of the vascular bundle- 

 cylinder, as in Pandaims and the Bromeliaceae, or cortical bundles may appear outside 

 the cylinder, as in many Palms, the rhizomes of Carex hirta, etc. More important 

 deviations also occur, for which De Bary's Comparative Anatomy must be consulted. 

 We will only add here that the vascular bundles are arranged in the leafy stems of 

 Tanms and Dioscorea Batatas as in Dicotyledons, that is, with the bundles in a circle 

 round the pith ; it has been already stated (p. 400) that the embryo in the Dioscoreaceae 

 resembles that of Dicotyledons in the growing point of the stem being apical, not lateral 

 as in most other Monocotyledons. 



The following systematic arrangement of the subdivisions of the Monocotyledons is 

 that of Eichler in his Syllabus \ The brief diagnoses of the orders are only intended to 

 point out a few of the characters which are important for purposes of classification. It 

 would be possible in the space here at command to describe each separate family of the 

 Monocotyledons ; but to do the same for the Dicotyledons would far exceed the limits 

 of this work, and for uniformity's sake therefore we must be content simply to name them. 



Series I. Liliiflorae. 



Inflorescences very various, racemose or cymose ; large flowers sometimes solitary' ; 

 flowers pentacyclic and trimerous, with a few exceptions of dimerous and tetramerous 

 or even pentamerous whorls ; inner staminal whorl wanting in Irideae ; perianth- 

 whorls usually similar, inconspicuous and glumaceous (Juncaceae), but usually both 

 petaloid (Liliaceae, Irideae, Taccaceae, Haemodoraceae, Pontederiaceae) and often 

 large, or outer perianth developed as a calyx, inner as a corolla (Bromeliaceae) ; 

 sometimes al six leaves cohering into a tube (Haemodoraceae, etc.); stamens often 

 epipetalous and episepalous ; ovary superior (Juncaceae and Liliaceae), superior or 



' Eichler, Syllabus d. Vorlesungen iiber specielle medicinisch-ph.armaceutischc 15ot:inik, Jiid 

 Ed. 1880. [The details of the anangement of the Monocotyledons given here and of the Dicoty- 

 ledons differ in some respects from those given by Eichler. For a more satisfactory arrangement 

 of the genera of Flowering Plants in orders and larger groups tlie reader is refcncd to Pentham and 

 Hooker's Genera Plantarum.] See also Warming, Handb. den >ystcmaliske hctaiiik, iS;^. 



