THE MEGASPOBANGIUM 63 



nous cells beneath parietal tissue occurs in Potamegeton (Wie- 

 gand, 54 Holferty 55 ), Triticum (Koernicke 33 ), Agraphia 

 (Vesque 12 ), Triglochin (Vesque 12 ), Lysichiton (Campbell 4T ), 

 Rosaceae, Saxifragaceae, many Leguminosae (as Lupinus, Cer- 

 cis, Acacia), Euphorbiaeeae, Cuphea ( Guignard 17 ), Fuchsia 

 (Vesque 12 ), Mesembrianthemum (Guignard 17 ), and doubtless 

 many other Monocotyledons and Archiehlamydeae. 



From a conspicuous development of parietal tissue there 

 is a complete gradation to its entire suppression. A few peri- 

 clinal divisions of the parietal cells may occur or none at all. 

 Sometimes in case the periclinal divisions have been abandoned, 

 one or more anticlinal divisions may be induced by the broad- 

 ening of the mother-cell, as the single periclinal division in 

 Typha ( Schaffner 36 ) and Lemma (Caldwell 46 ), and the series 

 of such divisions in Convallaria (Wiegand 54 ) and Butomus 

 (Ward 14 ). 



The gradation toward the suppression of parietal tissue 

 is further illustrated in cases where the primary parietal cell 

 divides or not in the same species, as in the grass Cornuco- 

 piae (Guignard 17 ), Pontederiaceae (Smith 40 ), Yucca' (Guig- 

 nard 17 ), and Thalictrum (Overton 59 ). The next stage is rep- 

 resented by the constant failure of the parietal cell to divide, 

 as in Alyssum (Miss Riddle 42 ) and Limnocharis (Hall 58 ). 

 The last case is of special interest from the fact that in the 

 cutting off of the primary parietal cell no wall is formed, and 

 tbe cell speedily disappears through the growth of the mother- 

 cell. 



The transition from an incomplete and ephemeral primary 

 parietal cell to none at all is natural, and this final stage, in 

 which there is complete suppression of the parietal tissue, has 

 been reached by many plants. It may be of interest to consider 

 how far this condition has been reached by the great groups. 



Among Monocotyledons the suppression of parietal tissue 

 occurs in all the higher families, but it is usually associated 

 also with the greater or less development of this tissue. Among 

 Gramineae, Cannon 50 reports Arena fatua as having no parie- 

 tal cell, although other Gramineae are known to possess it, and 

 in Triticum (Koernicke 33 ) it develops an extensive tissue. 

 Among Commelinaceae, Guignard 17 records Commelina stricta 

 as without a parietal cell, and Strasburger 13 figures Trade- 



