CBLL FOBMATION ST DIYI8I0N. 39 



(a) The foregoing must suffice as examples of Fission. It occurs 

 throughout the vegetable kingdom and may be regarded as the great 

 means by which cells are multiplied. 



(6) The cambium zone of Dicotyledons may be examined very profit- 

 ably by the student. If a tliin cross-section of a stem be soalied for a 

 Short time in a carmine solution, the protoplasm of the cambium zone 

 ■will be colored, and the newly formed partitions made thus more 

 distinct. 



(c) The ends of young roots are valuable for study ; longitudinal sec- 

 tions of these should be made, and treated as in the previous case. 



(it) Another interesting study of a special kind of fission may be 

 taken up in an examination of the development of stomata. (See p. 99.) 



(e) That slight variation of fission, which has sometimes been called 

 budding, may be very easily studied in the Yeast Plant {Saecharomyces 

 eerevisioB).* The conidia, stylospores, and basidiospores of many fungi, 

 which are more diflScult to study, are 

 very instructive examples of this va- 

 riety of fission. Conidia may be 

 studied in Cystopus ; stylospores in 

 the Red Rust of the grasses (ihe so- 

 called uredo-stage of Puccinia gram- 

 inis) ; and basidiospores in young 

 toadstools {Agaricus). 



El TiV, "V f "Plo-n-l- /C Fig. 29.— The Teast Plant, /Scrre/iai'O- 



ol- — XI16 X east irlainj (loClC- myces cerevisiw. a. rounded crlls 



charomyces cerevisim) furnishes fow?n?iS't^?:wo',V;l? rorof ''o™! 

 a yery simple example of Inter- ^^ 'X T^^fva^fof in I'^f^^t 

 nal Cell -Formation. Under ^Tot'Z ^'Lf^^ri^.l^^ 



certain conditions the cells grow danghter-cells ; a and 6 X 400, c and a 



° X 750.— After Beess. 



to a larger size than usual ; 



their protoplasmic contents divide into, generally, four 

 parts (two to four, according to Sachs), each of which 

 rounds itself up and secretes a wall of cellulose on its sur- 

 face (Fig. 29, c, d). Cells which divide in this way are called 

 mother-cells, and the new ones formed from them daughter- 

 cells. In the Yeast Plant after the daughter-cells are fully 

 formed the dead wall of the mother-cell breaks up. 



52. — The terminal cells of Achlya (one of the 8apro- 

 legniacem) form large numbers of daughter-cells by the 

 breaking up of the protoplasm, as shown in Fig. 30, A. 

 When the daughter-cells escape they become rounded {B,a); 



* See " Huxley and Martin's Biology," Chap. I. 



