Butters: seeds and seedling of caulophyllum. 19 



in length until it is about 35 mic. long. Its cytoplasm becomes con- 

 siderably vacuolate particularly in the lower part. The nucleus is 

 situated above the center of the cell and is of moderate size (about 

 12 mic. in diameter), densely granular, and vi^ith a distinct nucleolus. 



The first cell division in the embryo occurs from two to three 

 weeks after flowering (Figs. 3 and 4, PL IV). It is transverse, 

 and divides the embryo into dissimilar cells. The lower, or sus- 

 pensor cell is larger than the upper cell and has vacuolate cyto- 

 plasm. The nucleus is usually situated in the upper part of this 

 cell, and decreases in size as the growth of the embryo goes on. 

 The upper cell has denser cytoplasm, and usually a larger nucleus 

 than the suspensor cell. The succeeding cell divisions seem to be 

 quite irregular (Fig. 5-9, PI. IV). The primary suspensor cell 

 usually remains undivided, but it may divide in a plane perpendic- 

 ular, or somewhat oblique to the first division (Fig. 9, PI. IV). 



The upper of the two cells formed by the first division some- 

 times divides in a plane perpendicular to the first division. In other 

 cases this second division plane appears to be oblique to the first, 

 and cutting it at a more or less acute angle, while in a few cases 

 the arrangement of cells in a slightly older embryo indicates that 

 the upper cell divided transversely in a plane almost parallel to 

 that of the first division. Subsequent cell divisions are oblique, 

 and there is thus built up an oval or almost spherical embryo of 

 W'hich the suspensor cell or cells (when the primary suspensor cell 

 has divided) form at first about one-third (Fig. 11, PI. IV). The 

 cells adjacent to the primary suspensor cell gradually take on the 

 cytological characters of that cell, though they generally remain con- 

 siderably smaller than it. Their protoplasm becomes vacuolate, 

 and contains numerous highly refractive granules, their nuclei 

 decrease in size and stain more heavily. 



The cells in the distal portion of the embryo continue to divide 

 in all directions, and thus is gradually built up a pear shaped embryo 

 with a massive but somewhat slender suspensor (Fig. 12, PL V). 



The development of the embryo is slow, so that a month after 

 the flowering period, at a time when the seed is three-fourths of its 

 mature size, and the endosperm is developing rapidly, the embryo 

 has reached a length of only 150 mic, — less than one-twelfth of the 

 length of the embryo of the mature seed. It will be recalled that 

 at about this time the change takes place in the shape of the microp- 



