326 MORPHOLOGY OF GYMNOSPERMS 



grows very rapidly, soon inclosing the ovule, but the latter iSnally 

 grows above it, and at last it is only a light leathery sheath about the 

 base of the ovule extending half way to its tip. From this it would 

 appear that the outer integument or "aril" is a new structure, having 

 arisen in addition to all the old ones, and is not merely a dissociated 

 outer fleshy layer. That this new structure should frequently take 

 the character of this layer is not strange, for it holds the same general 

 relation to the seed; and among the podocarps the tendency to develop 

 the fleshy character extends far beyond the integuments. In Podo- 

 carpus it involves the bract on the stipe; while in Saxegothaea (150) 

 the scales of the strobilus enlarge and fuse into a globular fleshy 

 mass, much as in Juniperus. In the development of the stony layer, 

 the transformation of tissue begins at the apex of the integument and 

 gradually extends downward until it completely surrounds the 

 structures within. 



In Torreya the integuments are entirely free from the nucellus at 

 first, even after the mother cells are in synapsis. After that time 

 intercalary growth begins in the chalazal region and continues until 

 into the next season. As a consequence, in the mature seed the free 

 region of integument and nucellus is at the very tip, and is not more 

 than one-twentieth the total length of the seed. The same condition 

 exists in Taxus, and perhaps in most of the genera; while in Phyllo- 

 cladus the nuceUus and integuments remain entirely free. The vascu- 

 lar connections of the ovule in Torreya and in Phyllocladus, Micro- 

 cachrys, and Saxegothaea only are known, and the three latter genera 

 are probably representative of Taxaceae in general. In Torreya, 

 near the limit of the outer fleshy layer, there are two conspicuous and 

 opposite vascular strands; while in Phyllocladus, Microcachrys, and 

 Saxegothaea the vascular system ends at the base of the ovule. It 

 is to be expected that the distribution of the vascular strands should 

 depend upon the presence and position of a fleshy region in connection 

 with the seed. The seed of Torreya is regarded by Oliver (80) 

 as the most archaic of living conifers in its vascular anatomy. In 

 addition to the two vascular strands in the outer fleshy layer (outer 

 integument), the vascular plate at the base of the nucellus sends out 

 branches into the nucellus, which connect with a peculiar mucilaginous 

 layer that may represent the tracheal mantle of some of the paleozoic 



