Tendrils of Cucurbitacem. 249 



maintain the tendril as a spiral ; or, to state the case differ- 

 ently, it is a measure of the resistance to compression which 

 the softer tissues on the upper side of the tendril offer. 

 Obviously, the full strength can be maintained only so long 

 as the tension of the tissues is undisturbed, or until this 

 latter is replaced by hardening of all parts, when, as in all 

 old tendrils which have been for some time coiled, a new 

 element of strength is introduced. 



To more fully confirm the above results, numerous meas- 

 urements of the tendrils were made to determine the rela- 

 tive lengths of the inner and outer surfaces of the spirals, 

 or the general relation in length of the bast on the lower 

 side and the softer tissues above. The ratios obtained were 

 necessarily a little high for the true mean position of these 

 tissues, from the fact that all the determinations were made 

 from the inner and outer diameters of the spirals, and there- 

 fore relate wholly to the corresponding surfaces. The 

 results, however, will be found to harmonize well with 

 those obtained by a different method. The following will 

 sufficiently explain the results in ratios of the inner to the 

 outer surfaces : — 



Dimensions op Spirals. 

 Batios of Inner and Outer Surfaces. 



Cucurbita pepo. 



1:2.0 



10 - 



1:2.0 



11 - 



1 : 4.0 



12 - 



1:1.7 



13 - 



1 :2.0 



14 - 



1:2.7 



15 - 



1:1.8 



16 - 



1:1.5 





1:1.7 





1:1.8 

 1:2.7 

 1 :2.0 

 1 : 2.03 

 1 : 1.33 

 1 :5.2 

 1 : 2.2 



1 : 2.29 



In all of these it will be noted that the ratio increases or 

 decreases as the coils become closer or more open — a fact 

 which is most strikingly illustrated in Nos. 3 and 15, which 

 we may almost regard as exceptional cases. If they are 

 excluded from the general results, the mean ratio then 



11 



