220 BOTANICAL GAZETTE [SEPTEMBER 
grown cotyledons did not fuse, but 1 cotyledon is developed in 
the place formerly occupied by 2. The number of cotyledons is 
actually reduced by fusion of the primordia. 
A zygomorphic tendency, which is usually only very slight, is 
evident in nearly all mature embryos of P. Banksiana, but only 
occasionally in the early stages of the embryo. This zygomorphy 
of the matured embryo is, no doubt, a secondary result due to the 
shape of the seed, for it is always oriented within the seed in the 
same manner, and the zygomorphy is less pronounced in the case 
of P. Strobus, which has a more regularly shaped seed. The 
zygomorphic tendency found in some early embryos cannot be 
related to the shape of the seed, and is no doubt due to certain 
hereditary tendencies. The most extreme case found (text fig. 3L) 
was that of P. Laricio. When zygomorphy is pronounced, as in 
this case, it furnishes an interesting parallel to the development of 
certain monocotyledonous embryos at the stage when primordia 
develop, as shown recently by CoutTer and Lanp (11). In Pinus 
the zygomorphy never goes to such an extreme as in the mono- 
cotyledonous embryo, and no cotyledonary tube is formed in any 
of the pines that were studied. That we have well developed 
cotyledonary tubes among the Abietineae is shown by the work of 
Hitt and DEF RAINE (16) and by the recent work of HUTCHINSON 
(18) on Keteleeria. The cotyledonary tube would be formed 
as a natural accompaniment of a coalescence of the many cotyle- 
dons by fusion; its very existence among the historically recent 
gymnosperms is a further indication that cotyledonary fusion has 
taken place, rather than a splitting. It is interesting to note in 
this connection that the number of cotyledons in ‘Keteleeria is 4, @ 
rather reduced number. : 
Summary 
1. A special technique for dissecting ovules, staining and 
mounting the embryos, and an improved method of staining 
embryos in serial sections have been described in detail. 
2. The corrosion cavity results from an enzyme, which may 
be secreted by the unfertilized eggs as well as the embryo. 
3. Two forms of polyembryony must be recognized in gymno- 
sperms, namely, cleavage polyembryony and the polyembryony 
