CONIFERALES 355 



ing forms from polycotyledony to dicotyledony, in both conifers and 

 cycads. She believed that polycotyledony is the primitive condition. 



BucHHOLZ,^^"^^ studying a great number of species in critical 

 stages, concluded that polycotyledony is primitive, and that the 

 lower numbers are due to fusions. He lays little stress upon vascular 

 anatomy as a factor in this problem, because the primordia of the 

 cotyledons are well developed before any vascular structures appear. 

 He found that the average number of primordia in the younger em- 

 bryos, with fusing cotyledons bearing double primordia, was in ex- 

 cess of the average number found in the older stages, after any fu- 

 sions or spKtting of cotyledons had been completed. 



Forms with a large number of cotyledons, like the Abietaceae, 

 are primitive in other features; and forms with 2 or 3 cotyledons, like 

 some of the Cupressaceae, are advanced in other respects; but, of 

 course, this is not a very convincing argument. There is no doubt 

 that the number of cotyledons is sometimes reduced by the abortion 

 of one or more. It is not so easy to prove whether a primordium, 

 notched at the top, is splitting, or is the result of fusion. Buchholz'^^ 

 work seems to show a fusion (fig. 340). The fact that the primordia 

 are easily distinguishable before any vascular strands appear would 

 indicate that the vascular structures do not cause any spHtting. It 

 is certain that vascular strands, groAving faster than the surrounding 

 parenchyma, cause lobing, serration, and other margins of leaves; 

 but here, the strand is present at an early stage. In conifers the 

 primordia of cotyledons, appearing in advance of the strands, could 

 not be formed in such manner. 



After the proembryo breaks through the base of the egg the elon- 

 gating suspensor cell thrusts the embryo tier deeper and deeper into 

 the gametophyte. The base of the egg is partly dissolved and partly 

 fractured as the embryo goes through. In forms with cleavage poly- 

 embryony, the cells of the elongating suspensor, and also those in 

 the embryo tier at the tip, spht apart. The abundant starch grains 

 surrounding the embryo disappear, especially for a long distance im- 

 mediately in front, and their place is taken by soluble foodstuffs, 

 which are taken in by the rapidly growing embryos. 



The gametophyte tissue in contact with the embryo not only loses 



