108 Trans. Acad. Sci. of St. Louis. 



acid do not affect the cell-wall ; sulphuric acid and iodine color 

 it blue. 



Marslliaceae. Much interest has been manifested in 

 an anatomical study of the wall of the sporangium. This 

 structure has not always been emphasized by writers. Of the 

 numerous writers may be mentioned Bischoff (18, 1: 94, 2: 

 110); Mettenius (407); Luerssen (.398, 3:611, 619. /. 

 191)', Strasburger (446b, 123. ;;?. 8. f. 147-149); Valen- 

 tine (454); Hanstein (363. 365); Braun (305); Russow 

 (212); Mattirolo (401); Campbell (310. 311, 418. /. 

 217B). 



The structure of the sporangium has been treated by many 

 writers. An explanation of the light line was offered by 

 Mettenius, who published several monographs on this and 

 related orders of vascular cryptogams. In Marsilia quadri- 

 folia the light line extends across the middle of the Malpighian 

 cells. When treated with chlor-iodide of zinc the cell-walls, 

 including the light line, color bluish-black. With phloroglu- 

 cin and hydrochloric acid no reaction for lignin occurs in any 

 part of the cell. With concentrated sulphuric acid the cell- 

 walls are readily dissolved. With sulphuric acid and iodine 

 the walls color blue. The Malpighian cells are acted upon 

 much more readily than the other parts of the sporangium. 



Ecology and Physiology of the Malpighian Cells. — The 

 foregoing review shows that these cells occur in different 

 orders of plants, by no means always closely related. This is 

 an excellent illustration of the fact so frequently noted, that the 

 same structure recurs in different plants for the perpetuity of 

 the species. It is a well-known fact that the seeds of some 

 Leguminosae are extremely hard, e. g., Gymnodadus, Gle- 

 ditschia, Mucuna, and Physostigma. The seeds of Canna 

 are extremely hard ; so are those of Nelumho. AVe recall also 

 the hard seeds of Ceanothus and Gei'anmm, and the sporan- 

 gium of Marsilia. 



Functionally the testa of leguminous seeds, and the fruit of 

 some others, protect the seed against variations due to 

 changes of moisture. Many of the seeds of Leguminosae 

 retain their vitality for a long period of time. De Candolle 

 (49) found that the seeds of Leguminosae and Malvaceae 



