44 FLAM ril\SU>LiHi\ AM> 1XH)L(H;Y 



constant ratio botwoon ihr root syston\ :\\\d i\\c :\ov\:\\ p:irt of 

 \\\c plant is n(>1 noooSvsarily tnu\ Tlu^ at'tnal (^xioiit of ro(>t sys- 

 tems is well .shown by Nohbc's rosnlts wiili iMu^-yoar-old sooil- 

 lin^s >f tho pino and tho tiv. 'The fornuM- has a shallow ro(>t sys- 

 toni. tho latter a dct^p-soatod oiuv TluMoial lons;th of roots in ilu^ 

 pine was fomul ti" be 12 meters, and in llu^ lir 2 meters. Vho sm- 

 face area of ilu^ V(>(>ls was 2('>() s(]|. cm. in the pint\ and I() sq. cm. 

 in llu^ lir. The i^s(imati\l leni:;lh oi []\c roo\ syst(Mn o\' maturt* 

 grains is !\00 m.. anil oi a lariie w att^'nu^lon vim^ 2o kiliMniMers. 

 In vig'orons water plants, on llu^ contrary, ihe eniin^ roi>i sysliMn 

 mt\'ism-(^s bnt ;i very f(n\- meters. 



Experiment 6. Sttucturo of llio root unit formation of root hairs. 

 Place seeils of the g.-n-dcn sunlUnviM- in two gcrnun.-itors, one of which 

 is nearly tilled with w;vt<M-, ihc other containinji; b.arely eiunisih water 

 to keei> the air nu>ist. When tlu^ roots rca(>h 2 cm. in length, cut thin 

 cross- and longi.seclions oi ouo or two n^ots from c;ich uim inin.'itor. M;dvc 

 !\ del. 'died dr.'wvine; of .\ sciiiniMit rcachini;' to ihc noddle of llu^ cro.ss- 

 sectitui, and <^f (>ne cxtendiui!; across the longisection, indiciUin"; the 

 v:vri(>us rciiii>ns and 1 issues. ]\le;vsurc .'nul dr;vw a typic;d nioldiair, 

 compntinii' ;ds(>its surface. From coimts of the cross- and lonjiiscctions, 

 est innate the nund>cr of root-hairs on a root taken from each sierminator. 

 With the surl'.'uv iif thi^ ri>ot-h.iir .di-(\'ul>' mensm-<Nl .-is a basis, compute 

 the total absorbiuii' .vrea oi cm'U voo\ . 



Experiment 7. Hyiirotropism. iMubml a porous lube or a 2-inch pot 

 without a hole in the biittom, in the middle of a (>-inch pt^t tilled with 

 soil, ^loistcn the soil sliijhtly. .and pl.anl simtlower seeds in it. Place 

 the seeds ocfu.-vlly distant from thi^ iNls:;es of \hc p(>1s in sui'h m;inni>r that 

 llie emiM-giuii' ri>i>ts will st;ni io sirow in .-dl directions. Fill the ]>orous 

 tube with water. .V few days after the ci>tyleilons ajipear, disj up the 

 seedlin<;-s c;ircfully, noting the piisititin of the niots. :md the region in which 

 the tm'ning occurs. 



57. Imbibition. This is the process th.at t.akes pl.ace when a 

 si^lid or semi-soliil absiirbs water. It is due to the .attraction 

 which the moUvnles of tho two snbstaneos ha\e fiu- each other. 

 This in some dei;ree o\ erctMnes the cohesion of the molecide^s 

 of the solid, causing them to separ.ate and the si>lid \o swell. The 

 swelling due to imbibition can be re.adily measured, ami during 

 the process it can be easily shinvn that a largo amount of work 

 is being done. Tho swelling line to imbibition is most pronounced 

 in the dead or resting tissues of ]>lanls, but it c.an also be detectoii- 

 in living cells. 



