Systematic Atavism 645 



loose one disperses them. According to such 

 fluctuating deviations the number of leaves, in- 

 serted upon a given number of spiral circuits, is 

 different in different species. In a vast major- 

 ity of cases 13 leaves are found on 5 circuits, 

 and as we have only to deal with this propor- 

 tion in the teasels we will not consider others. 



In the teasels this screw-arrangement has dis- 

 appeared, and has been replaced by a decussate 

 grouping. The leaves are combined into pairs, 

 each pair occupying the opposite sides of one 

 node. The succeeding pairs alternate with one 

 another, so as to place their leaves at right 

 angles. The leaves are thus arranged on the 

 whole stem in four equidistant rows. 



On the normal stem of a teasel the two mem- 

 bers of a pair are tied to one another in a com- 

 paratively complicated way. The leaves are 

 broadly sessile and their bases are united so as 

 to constitute a sort of cup. The margins of 

 these cups are bent upward, thereby enabling 

 them to hold water, and after a rainfall they 

 may be seen filled to the brim. It is believed 

 that these little reservoirs are useful to the 

 plant during the flowering period, because they 

 keep the ants away from the honey. Consider- 

 ing the internal structure of the stem at the base 

 of these cups we find that the vascular bundles 

 of the two opposite leaves are strongly con- 



