CELL FORMATION BT DIVISION. 39 



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

 tlirougbout the vegetable kingdom and may be regarded as the great 

 aieans 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 soaked 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 treatedias in the previous case. 



(rf) 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) Tliat slight variation of fission, which has sometimes been called 

 budding, may be very easily studied in the Yeast Plant (Saccharomyces 

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

 which are more diflftcult to study, are 

 very instructive examples of this va- 

 riety of fission. Conidia may be 

 studied in Oystopus ; stylospores in 

 the Red Rust of tlie grasses (the so- 

 called uredo-stage of Puccinia gram- 

 inia) ; and basidiospores iu young 

 toadstools (Agaricus). 



rri, v J- T>1 4- f V -^'S' 29.— The Yeast Plant, Saccharo- 



51. — Xlie xeast Jrian'C \OCtC- myces- cerevisice. rt, rounded cells 



7 „ „„„ ..■„/„\ 4',n.,.v,icl,^c. from " bottom yeast," 60 hours after 



charomyces cerevisim) larnislies sowing in beer-wort; », row of ovai 



a yery simple example of Inter- f^, 'S :Xl^\:. I'X^ft 



nal Cell -Formation. Under ca^t four ceii^s^fo™^ 



certain conditions the cells grow <^*?f "«'":''?"* i " ""* * x ^"O' " """^ '^ 



X tuUi — Alter xCsims. 



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 Aohlya (one of the Sapro-. 

 legniacea) 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. 



