GENERAL RESULTS— PTEROPSIDA 649 



Seeds of the Trigonocarpus type (p. 452), referable 

 to Medulloseae, appear to have much in common 

 with those of the Cycadaceae, as shown by the drupe- 

 like differentiation of the testa, the double vascular 

 system, and the form of the pollen-chamber. The 

 chief difference lies in the free nucellus of the Trigono- 

 carpeae, which contains the inner vascular system, 

 whereas in the Cycadaceae the nucellus is adherent 

 to the integument, and the inner vascular system 

 is said to belong to the latter — a point exceedingly 

 difficult to determine. In spite of these differences, 

 I am inclined to regard the Trigonocarpus type as the 

 nearest approach among Pteridosperms, so far as we 

 know at present, to the seed of the Cycadaceae. 



Anatomically, the Medullosean stem differs from that 

 of recent or Mesozoic Cycadophyta in being polystelic 

 (except in the protostelic Sutcliffia, which does not 

 affect the question). Certain local peculiarities in the 

 vascular system of various Cycads, due to anomalous 

 distribution of the cambium, have recently been 

 interpreted as relics of a polystelic structure, but these 

 exceptional irregularities do not appear to bear more 

 than a superficial resemblance to the primary polystely 

 of the Medulloseae. 1 



On the other hand, the structure of the petiole and 

 the organisation of the leaves generally are very similar 

 in Medulloseae and Cycadaceae, and the resemblance 



1 Some of the most striking cases of so-called " polystely " among recent 

 Cycads occur in the root, an organ which in the Medulloseae was mono- 

 stelic. For the polystelic interpretation of Cycadean structure see Wors- , 

 dell, "Structure and Origin of the Cycadaceae," Ann. of Bot. vol. xx. 

 1906, p. 129; Matte, Richerches sar I'appareil libera - ligneux des 

 Cycadacies, 1903. 



