358 PROLIFEEOUS OE VIVIPAROUS PLANTS. 



Festuca ovina, var. vivipara, Aira caespitosa, var. alpina, Poa alpina, 

 etc., as well as in Alliums, Trifoliums, and Ferns. Buds of a similar 

 kind may be produced on the edges, or in the axil of leaves, as in 

 Bryophyllum calycinum, Malaxis paludosa (fig. 231, p. 118), many 

 species of GeSnera, Gloxinia, and Achimenes ; and the bulbils of Lilium 

 (fig. 230, p. 117), Ixia, Dentaria, Ornithogalum (fig. 232, p. 118), 

 some Saxifrages (S. cernua and S. foliolosa), seem to be peculiar 

 forms of buds, capable of being detached, and of assuming indepen- 

 dent growth. Buds, however, difier from true embryos in the 

 direction of the roots being towards the axis of the plant. In uni- 

 cellular plants, and others of the lowest class, it is common to find 

 each cell possessing the power of producing a new individual, either 

 by simple division or by the formation of a cellular bud. In higher 

 plants this mode of propagation is carried out by means of an assem- 

 blage of cells, which are developed into an organ or bud of a more 

 complicated nature, before it is detached. Multiplication by division 

 of cells is very common among the lowest Algae, such as Desmidiacese 

 and Diatomaceae (fig. 472, p. 267). In the case of Lichens, the 

 thallus produces gonidia (p. 269), which appear to be a collection of 

 cellular buds capable of producing independent individuals. On the 

 thallus of Liverworts (Marchantia) cup-like bodies are produced con- 

 taining gemmae (fig. 488 g, p. 275). In Mosses the power of repro- 

 duction by gemmae is very marked. Almost every cell of the surface 

 of Mosses, according to Sohimper, is capable of giving origin to a leafy 

 plant . or innovation. Ferns are propagated by buds, and gemmae 

 occasionally occur on their prothallium. The higher classes of plants 

 may be considered as consisting of numerous buds united on a common 

 axis (fig. 219, p. 109). These possess a certain amount of independent 

 vitality, and they may be. separated from the parent stem in such a 

 way as to give origin to new individuals. In some instances buds 

 are produced which are detached spontaneously at a certain period of 

 a plant's life. The cloves formed in the axils of the scales of bulbs 

 are gemmae or buds, which can be detached so as to form new plants. 

 The length of time required for the protrusion of the radicle varies 

 in different plants. Some seeds, as garden cresses, germinate in the 

 course of twenty-four hours, others require many days or many months. 

 Seeds with hard coverings, or a stony perisperm, may lie dormant in 

 the soil for a year or more. The following experiments were made in 

 the Geneva garden, on seeds similarly watered, and exposed to a 

 medium temperature of 53° F. It was ascertained that one-half of 

 the species of the following families germinated after the lapse of the 

 number of days here mentioned : — 



Amarantacese 9 days. 



CruciferiB ........ 10 „ 



BoraginaceEe, Caryophyllaceas, Chenopodiaoeae, Malvaceas . 11 „ 



