PHAJ^EKOGAMIA. 451 



of minute laminae, gi'anules, or spiculae embedded in its sub- 

 stance, or as an encrusting layer on the outer or inner side of the 

 cell, — the author's observations establish the first condition ; the 

 question, however, as to the precise mode of union of the silica 

 with the membrane, whether there is a chemical combination 

 between them, or a mechanical deposition of silex between the 

 molecules of cellulose, is left for chemists to determine. It is 

 shown that the deposition of silica certainly takes place in liviug 

 and even growing organs, contrary to Criiger's opinion that 

 tissues do not become siliceous during active life. From the shields 

 of Diatomaceae, which Kiitzing believed to consist of pure silica, 

 H. V. Mohl finds an organic membrane, retaining the foi*m and 

 markings of the valve, to remaia after removal of the silica by 

 fluoric acid. The cells of the mesophyllum and also the vascular 

 bundles of leaves are found sometimes to be more or less silicified ; 

 yet, between the siliceous character of the epidermis and that of 

 these inner tissues, there is no constant relation. In many plants 

 with a strongly silicified epiderm, no trace of silica is found in the 

 veins and midrib, while on the other hand, the vascular bundles 

 may have a large deposit of silica, as in the Oak, Beech, &c., 

 while the epidermis is but very slightly silicified. Observations 

 are added on the occurrence of siliceous masses or nuclei in the 

 cavity of the cells, as observed by Criiger. 



Mohl, H. von. — Eiu Beitrag zur G-eschichte der Keimuug. Bot. 

 Z, 1861. p. 257. 



The author finds in the albumen of Pinus Pinea, and Ricinus 

 communis during germination, a change of the oily cell-contents 

 into sugar, through an intermediate stage of starch formation, 

 as in the case of embryos had been previously remarked by Dr. 

 Sachs, who, however, failed to observe this sequence of change 

 in the albumen of Ricinus, 



The exceptional character of starch formation as a transi- 

 tional stage in the formation of sugar from the fatty oil of the 

 albumen, suggested the probability that it might stand in con- 

 nection with a growth of the albumen, which measurements 

 of germinatuig seeds of Ricinus showed to be the case. The in- 

 crease in bulk is shown not to be dependent on the hygroscopicity 

 of the albumen cells, but to be due to an actual growth. H. v. 

 Mohl confirms Dr. Sachs' observation of the formation of Chloro- 

 phyll in the cotyledons and upper part of the axis of germinating 

 plants of Pines notwithstanding complete exclusion of light. 



— — — Nachtrag zu dem Aufsatze iiber des Kieselskelett lebender 

 Pflanzenzellen. Bot. Zeit. 1861. 305. 



The author finds siliceous deposits in 42 Natm-al Orders. 

 Species are enumerated in which both the epiderm and vascvdar 

 bundles of leaves were silicified, also those in which silex was 

 found in the e])iderm only. In connection -with the unequal 

 distribution in the epidermis of sUex and its deposit in more 



