158 COMPENDIUM OF GENERAL BOTANY. 



I. Monocarpous plants (haplobioticce) bear fruit only once and 

 then die. This occurs in one year in annual plants, in two years in 

 biennial plants ; in some after four or five years, as, for example, 

 the 'Agave americana. (In our greenhouses this plant bears 

 flowers only after about forty to sixty years.) 



II. Polycarpous plants (anabioticce) regularly form fruit each 

 year on one and the same plant- body. Two means serve to main- 

 tain the plant-species: the periodical formation of seed, and the 

 longevity or endurance of the plant. These plants may again be 

 divided into two groups : 1, the aerial stem is woody and endures 

 as such for a long time, as, for example, shrubs and trees, some of 

 which are evergreen, while others drop their leaves ; or 2, the stem 

 is herbaceous and dies to the surface of the soil each year, but begins 

 to grow again from a subterranean perennial stem. These are the 

 perennial plants in the narrower sense, and in them occur the above- 

 mentioned subterranean stem-modifications which serve as reservoirs 

 for reserve food-materials (starch, water, albumen, etc.). Typical 

 rhizomes occur among grasses and species of Carex ; bulbs among 

 Liliacece, tubers of Solanum tuberosum (potato). " Runners " may 

 serve as asexual propagative organs ; that is, prostrate lateral 

 branches which have developed from subterranean buds may 

 develop roots, stems, and leaves from the nodes. 



Some of the aerial stem-modifications receive special names. 

 The culm of grasses is a hollow stem with nodes at the attachment 

 or insertion of the leaf and usually branching near the apex. The 

 flower-stalk is nearly always free from leaves and terminates in a 

 single flower or group of flowers. The culm of semi-grasses (Cyper- 

 acecB) contains pith and is without nodes. There are tubers with 

 one or several buds, depending upon the number of internodes 

 represented. The potato has many buds situated in depressions 

 and surrounded by scaly leaves. A peculiar case of a tuber with 

 one bud is where the hypocotyledonous member, that is, the portion 

 of the stem below the cotyledons, becomes thickened, as in the 

 horse-radish. 



The conception " tuber " is purely morphological, as is seen from 

 the fact that orchid-tubers 1 are thickened secondary roots. In 

 Spiraea filipendula secondary roots also become much enlarged. 



1 The more precise morphology designates these as " tuberidia " instead of 

 '' tubers." These organs furnish the officinal mucilage of salep. 



