1918] BUCHHOLZ—PINUS 213 
cause may also account for the variation in the time of appearance 
of the vertical walls in the initial cells of the early embryonal tubes. 
STRASBURGER (38) also cites the case of an embryo similar to 
fig. 21a as disproving the constant existence of an apical cell, but 
fig. 21a has an apical cell; it is one of the 4 cells of the apical tier, 
one of the adjacent cells is its last segment, while the two remaining 
cells constitute the next older segment. 
An embryo like fig. 21a, but in which the e, tier of cells has 
elongated, looks so much as though it shows the original 4 embryonal 
cell rows going into a single embryo that doubtless this impression 
could be created from a study of serial sections only. When STRAS- 
BURGER found a stage very similar to fig. 21a, however, he was 
able to trace the suspensor back to a single tube and recognize that 
it is only one-fourth of the product of the egg. According to his 
explanation the embryo from this stage on develops like that of 
Picea, in which the whole of the fertilized egg unites to form 1 
embryo, and has no apical cell. All of my investigations have failed 
to support this view, but, on the contrary, embryos slightly older 
than fig. 21a, such as figs. 16, 18, 22, and 28, always have an apical 
cell, and this cell may usually still be found in embryos of 500 or 
more cells.‘ Certainly the instances where the apical cell cannot 
be found in embryos having several hundred cells or less are rare, 
and the most exceptional cases found in this investigation have 
been figured and described. Every essential condition for an 
apical cell is satisfied. It has the proper position on the embryo, 
being at or near the apex of a body with polar differentiation; it 
has the same general shape as the apical cell at the stem tip of a 
fern; and it has recognizable segments which may be related in their 
regular turn to the 3 cutting faces, even in some embryos of 800 
ce 
From a comparative study of the embryos of other conifers it 
is probable that this apical cell feature is retained more generally 
than one would suppose. According to STRASBURGER (38) the 
Cupressineae all have this feature. CoKeEr’s (7) study of the 
embryo of Taxoedium does not conflict with this view, for in many 
* Estimated roughly by counting the average number of cells in diameter and 
length and applying the formula /r?. 
