xm] POLYSTELY 181 



secondary thickening. Both Auricula and Gunnera have near 

 relatives which are aquatic in habit. The reduced aquatic stele 

 of the submerged stem of Hottonia has much in common with an 

 individual stele of Auricula. This comparison between Hottonia 

 and Auricula has had its force greatly increased by Prankerd's 1 

 subsequent discovery of a transient polystelic phase in Hottonia 

 palustris in the base of the inflorescence axis that is to say, 

 in the region of transition from an aquatic to an aerial type of 

 stem. 



It was observed by Scott that the stele of Myriophyllum or 

 Hippuris agrees closely in structure with that of the monostelic 

 Gunneras, or with a single stele from one of the polystelic 

 species. The comparison of the stele of Myriophyllum with that 

 of the Gunneras has been fully confirmed by more recent work 2 . 

 In the case of Gunnera assuming a descent from an aquatic 

 ancestor it is easy to realise how acute the need for increased 

 vascular tissue in the rhizome must have become when the 

 present type of habit was acquired, since the leaves grow in some 

 cases to an enormous size. Darwin 3 , in the Voyage of the 

 Beagle, describing the occurrence of Gunnera scabra on the 

 Island of Tanqui, off Chili, remarks " I measured one [leaf] 

 which was nearly eight feet in diameter, and therefore no less 

 than twenty-four in circumference! The stalk is rather more 

 than a yard high, and each plant sends out four or five of these 

 enormous leaves, presenting together a very noble appear- 



ance." 



It should be noted that Scott had overlooked one previous 

 record of polystely due to Dangeard and Barbe 4 that of the 

 occurrence of four or five steles in the axis of Pinguicula vul- 

 garis. But this case introduces no difficulty so far as Scott's 

 hypothesis is concerned, for Pinguicula is related to Utricularia 



1 Prankerd, T. L. (1911). 



2 Schindler, A. K. (1904). This author takes the view that Hippuris 

 does not belong to the same cycle of affinity as Gunnera and Myrio- 

 phyllum. 



3 Darwin, C. (1890). 4 Dangeard, P. A. and Barbe, C. (1887). 



