328 M. Miiller on the Germination of Isoetes lacustris. 



But it is perfectly clear from all this that so many pollen- tubes 

 are not necessary for the formation of any given number of 

 embryos. 



The formation of the embryo in Isoetes, or in the Lycopodiacea 

 generally, must also be of interest in other ways in regard to that 

 of the sexual plants. In Isoetes no pollen-tubes penetrate, and 

 yet the embryo-cell is developed independently. In the sexual 

 plants a pollen-tube must first have entered, before that cell can 

 be formed. I here of course assume that the indulgent reader 

 agrees with me that the germinal cell first originates in the em- 

 bryo-sac after the penetration of the pollen-tube in the sexual 

 plants ; in favour of which I have already elsewhere furnished 

 my observations *. This appears to me capable of explanation in 

 a consequential manner. In Isoetes the ovule contains the true 

 protoplasm, from which may be developed a peculiar mother-cell 

 like that of the embryo ; in the sexual plants this matter is not 

 present in the embryo-sac. It must be furnished in a different 

 way and is brought by the pollen-tube. 



In conclusion, let me hope that I have succeeded in the fore- 

 going pages in exhibiting, fulfilled and completed, the three prin- 

 cipal objects of these investigations, which I mentioned in the 

 introduction : how far Isoetes and Selaginella are allied in their 

 course of development ; how the peculiar formation of the root 

 takes place in Isoetes ; and how the uteral formation of the em- 

 bryo in an asexual plant is related to that of the sexual plants. 



EXPLANATION OF PLATES II. & III. 



N.B. The Numbers 5, 20, 50, 250 and 400 give the enlargement of the 

 object. 



Fig. 1. An ovule with the two outer coats just burst, and the coat of the 

 nucleus (a) visible. 



— 2. This last magnified to show its peculiar structure. 



— 3. The great papilliform cell with the contiguous cells, magnified. 



— 4. The granular contents of the ovule. 



— 5. The same converted into starch. 



— 6. The latter transformed into protoplasm. 



— 7. a, b. The first or embryo-cell. 



— 8. b. The same. c. A free cytoblast. d. A cytoblast around which the 



membrane is formed. 



— 9. a, b, c. The embryo-cell now become a cellular corpuscule. c. 



Treated with iodine to show how the cell-membrane of the mother- 

 cell incloses the cellular contents like a sac. 



— 10. a. The embryo, becoming elongated, b. A single cell with cyto- 



blastema. 



— 11. The same. a. Alimentary organ, b. Vagina, c. Cell of the first 



scale ; all just begun to be developed. 



* Bot. Zeitung, 1847. Beit. z. Entwicklungsgesch. d. Pflanzen-embryo, 

 p. 737 et seq. 



