280 THE PHENOMENON OF 



these layers appears to take place with especial regularity 

 in the Graminacea3. According to Hofmeister's ob- 

 servations,* the nuclei imbedded in the mucilaginous 

 layer which lines the embryo-sac arrange themselves with 

 a certain regularity, becoming distributed at equal dis- 

 tances on the inside of the wall of the embryo-sac.. As 

 a cell is formed around each of these nuclei, and on all 

 simultaneously, the embryo-sac becomes lined with a 

 layer of cells, the first of the endosperm. On the inside 

 of this a second layer of cells is soon deposited in a similar 

 manner ; this is followed by a third, and so on. Leaving 

 out of view the lamellar repetition, this process of cell- 

 formation clothing the wall reminds us very much of that 

 examined under D. 2 ; the exhaustion of the contents of 

 the embryo-sac (i. e. the mother-cell) occurring with the 

 formation of the last, innermost endosperm-cells, is related 

 to D. 1. 



When we consider the whole of the phenomena of 

 cell-formation in the embryo-sac connectedly, we behold 

 the case, unique in its kind, of a mother-cell in which 

 different kinds of daughter- cells are produced at different 

 periods. None of these daughter-cells belong any more 

 to the tissues of the mother-plant ; all, as cells originating 

 free, are in a certain sense reproductive cells, new indi- 

 viduals ; but of the many sisters, only one, the first-born, 

 is ordinarily destined to become perfectly developed, 

 while the majority of the others are compelled, in their 

 earliest childhood, to perform nursing-service to the 

 chosen one. The difference of the cells formed in the 

 embryo-sac may indeed be compared with the occurrence 

 of bimorphous, partly fertile, partly sterile gonidia in 

 the Algas ; the parenchymatous conjunction of the ori- 

 ginally free endosperm-cells reminds us of the regular 

 combination of the previously free gonidia of Hydro- 

 dictyon and Pediastrum. 



exal(ata-) also Hofmeister, 1. c., t. xii, f. 25 (Polygonum orientate;) aud 

 t. xiii, f. 21, (Helianthus annuus.) 



* L. c., p. 30, t. xi, f. 25, 26, 29, (Sorghum bicolor.) 



