cook: morphology and evolution of leaves 537 



The Fe 2 3 fragments in the preparation containing 10 molecu- 

 lar per cent CaO, which had been heated to 1250° but was not 

 completely melted, had a variable and lower refractive index 

 than pure hematite (w as much as 0.05 lower). This is due to 

 solid solution either of CaO . Fe 2 3 or of Fe 3 4 . co was measured 

 in an amorphous mixture of selenium and arsenic selenide(As 2 Se 3 ), 

 by means of which, with the addition of tellurium, a refractive 

 index of about 3.15 for red can be reached. 



We have found no evidence as yet of a 3 : 1 compound anala- 

 gous to tricalcium aluminate. Samples of this composition 

 quenched 7 after 15 minutes at 1575°, 15 minutes a„t 1525°, 15 

 minutes at 1325°, and 3 hours at 1375° all consisted only of CaO 

 and 2CaO . Fe 2 3 . Thermal curves on this mixture showed only 

 the melting at 1434-1436°. 



Chemical analogy has naturally led several authors to expect 

 a phase rule diagram for the system CaO — Fe 2 3 similar to that 

 for CaO — A1 2 3 . Campbell, 8 for instance, assumed the exist- 

 ence of the compound 5Ca0.3Fe 2 3 , analogous to the 5 : 3 com- 

 pound of lime and alumina, and claimed to have found chemical 

 evidence for its existence. We find no evidence of such a com- 

 pound. Instead of being analogous to CaO — A1 2 3 , the dia- 

 gram of the system CaO - Fe 2 3 resembles that of MgO - Si0 2 9 

 much more clearly than it resembles that of any other of the 

 silicate systems with which we are familiar. 



PLANT MORPHOLOGY.— Morphology and evolution of leaves. 

 O. F. Cook, Bureau of Plant Industry. 



In seedlings of many palms, grasses, and other plants the first 

 leaves are simple, bladeless sheaths, or the blade appears as an 

 appendage or expanded outgrowth from the rim of the sheath. 

 Leaves with larger blades are produced as the plant grows, until 

 the adult degree of specialization is attained. The essential fea- 

 ture of the primitive leaf is the basal sheath, in the form of a 



7 Quenchings by G. A. Rankin. 



8 E. D. Campbell. Jour. Ind. Eng. Chem., 7: 835-837. 1915. 



9 N. L. Bowen. Am. Jour. Sci., 37: 487-500. 1914. 



