42 



Elementary Plant Physiology. 



its rate of elongation by llie method described in § i, and 

 note tlie manner in \\h\c\\ the cotyledons burst the integument. 

 Measure the cotyledons into intervals of 5 mm. on a line drawn 

 longitudinally, and on another drawn transversely, through the 

 center. Note the regions of greatest growth and the total 



amount of enlargement 

 (Figs. 21 and 22). Do all 

 cotyledons behave in this 

 manner ? 



36. Germination of 

 peas. — Soak some peas 

 {Pisuni) in water for a 

 day, then place in moist 

 sawdust, and make daily, 

 dissections. Note struc- 

 ture of swollen seed. 

 The hemispherical coty- 

 ledons, filled with reserve 

 material, are inserted on 

 the short hypocotyl, at 

 the lower end of which 

 may be seen the rudi- 

 mentary root. Follow the 

 comparative growth of 

 the root and shoot. Com- 

 pare the origin of the 

 root-hairs and secondary roots with those of the plants previ- 

 ously examined. 



Compare the fate of the cotyledons with those of the Ricinus. 

 Note the unequal growth of the young stem by which it is arched 

 as it is pushed up through the soil. (See " Epinasty and hypo- 

 nasty.") Mark off intervals on the stem, and ascertain the rate 

 and region of growth (Figs. 21 and 22). 



The earlier leaves formed on the stem are seen to be simple 



Fig. 22. — Advanced stages of germination 

 of Ricinus (A) and Pisum (B). ?-, root system ; 

 rfi, main root ; rs, secondary roots ; J>a, pa, 

 root-hairs ; ah-, hypocotyledonary axis ; c, c, 

 cotyledons ; i, insertion of cotyledons ; /, 

 stem ; y, leaves. After Bonnier and Leclerc 

 du Sablon. 



