Miscellaneous. 483 



2. This epigonium or nucleus is lined by a membranous embryo- 

 sac. 



3. The embryo developed in this ovule is represented by the cap- 

 sule with its pedicel. 



4. The nucleus and the embryo-sac are closed at first and open a 

 little before fecundation. 



5. The embryo-sac contains a free vesicle which produces the em- 

 bryo by its development. This embryonal vesicle exists before the 

 opening of the nucleus and consequently before fecundation. 



II. Riccice. — 6. In the Riccise there exist a nucleus, an embryo- 

 sac, and an embryonal cell exactly like those of the Mosses. This 

 embryonal cell, however, instead of producing a capsule with its 

 pedicel, merely becomes enlarged, and the sporiferous cells are formed 

 immediately in the interior of this membranous sac, which is itself 

 enveloped by the epigonium. 



III. Ferns. — 7. The Ferns have ovules exactly like those of the 

 Mosses and Hepaticse, also consisting of a nucleus formed of a simple 

 layer of cells and lined internally by an embryo-sac. 



8. In the Ferns these ovules are produced on a very simple frond, 

 which is the immediate result of the germination of the spores. The 

 embryo which is formed in these ovules reproduces the original plant, 

 as in the Phanerogamia. 



9. The ovule or nucleus of the Ferns is at first closed at the apex 

 and opens for fecundation ; it contains before its opening an embryonal 

 cell which produces the embryo by its development. 



10. The embryo of the Ferns consists of a primary leaf, a primary 

 root, and a conical base representing the stem or the axis of the 

 plant. The primary root is not a continuation of the stem as in the 

 embryo of the Phanerogamia ; it is oblique, and from this character 

 the embryo of the Ferns may be called plagiorhizal. 



1 1 . This character still exists in the developed plant. Each leaf has 

 its proper root, which separates almost immediately from the stem, 

 and takes an oblique direction towards the earth. 



12. In the Ferns, Mosses and Hepaticse, the base of the embryo 

 is turned towards the base of the ovule, and the apex towards its 

 summit or micropyle ; so that it is in a position the reverse of that 

 which it occupies in the Phanerogamia. — Comptes Rendus, Dec. 13, 

 1852, p. 851. 



MODE OF DETERMINING THE OPTICAL POWER OF A MICROSCOPE. 

 BY PROFESSOR HARTING OF UTRECHT*. 



The optical power of a microscope may be said to consist of three 

 qualities, viz. magnifying power, defining power, and penetrating 

 power. Although the first is the quality to which most importance 

 is generally attributed, the practised observer well knows that it is of 

 far less consequence than the second and third. And although there 



* Translated by the Editor of the Monthly Journal of Medical Science, 

 from ' Het Mikroskoop,' vol. i. p. 407. 



