194 BOTANY PART i 



two kinds of individuals, which regularly alternate with one another, 

 are frequently very different in form and structure, and bear different 

 reproductive organs. The reproduction of the one generation (sporo- 

 phyte) is asexual ; that of the other (gametophyte) is sexual. The 

 Fern may be taken as a typical example. The leafy fern plant is 

 the sporophyte, and produces only asexual spores. The spore on 

 being shed does not grow into a new fern plant, but into a small 

 thalloid structure .known as the pro thallium (Fig. 97), which is 

 the gametophyte, and reproduces sexually. The fertilised egg-cell 

 develops into a leafy fern plant. The reproductive cells of the one 

 generation give rise to the other generation, and there is thus a 

 regular alternation of the sporophyte and gametophyte. The two 

 generations may, however, as in the case of the Brown Alga, Dictyota, 

 resemble one another. 



Frequently the two generations are not represented by inde- 

 pendent individuals, but the one remains permanently connected to 



the other like a parasite on its host plant. 

 Careful investigation may then be required 

 to establish the existence of an alternation 

 of generations. This is the case for the 

 Bryophyta and the Seed-plants. 



Both generations may be able to reproduce 

 their like by vegetative reproduction. Multicellular 

 gemmae formed on the prothalli of some ferns grow 

 into new prothalli ; on the fern plant bulbils, 

 which grow into new leafy plants, may be 

 produced. 



1. Multiplication by Multicellular 

 Vegetative Bodies (Budding) 



This occurs in many Bryophyta, e.g. in 

 Marchantia, where the gemmae are formed 

 in special receptacles on the thallus (Figs. 

 444, 445). It is also widely spread in 

 the form of budding in Pteridophyta and 



FIG. 223. Shoot of Dentaria bulbi- Phanerogams. 



/era, bearing bulbils, br. (Nat. 



size. After SCHENCK.) Specially-formed lateral shoots serving to repro- 



duce the plant are seen in the runners or stolons 



produced above or below ground by many plants. The RUNNERS of the Strawberry 

 are slender cylindrical branches from the axils of the leaves of the rosette ; they 

 root from the terminal bud, which becomes independent by the subsequent decay 

 of the runner. Many BULBS and TUBERS serve for reproduction in the higher plants, 

 as do also BULBILS (Fig. 223) and the winter buds which become detached as the 

 HIBERNACULA of a number of aquatic plants (e.g. Hydrocharis, Stratiotes}. 



Buds may also arise in places where no growing points are normally present ; 

 they are then adventitious. Such buds are most commonly found on leaves, 



