Seedling Structure of Gymnosperms. II. 
223 
Diagram 7, and Fig. 3, PL XV), and the smaller portion often died away so 
that the strands finally performed as those of half-cotyledons ; in other cases 
the smaller portion of the divided bundles persisted, so that notwithstanding 
the unequal division the strand behaved right through as that of a whole 
cotyledon. 
Thus we have instances of cotyledonary bundles with intermediate 
characteristics, and these we consider examples illustrating the promotion 
of seed-leaves from a lower rank to a higher. There is thus no difficulty in 
the conception of the origin of a polycotyledonous from a dicotyledonous 
seedling by the process of splitting and promotion. 
At the same time, we do not desire to maintain that this is the in- 
variable rule : tricotyledonous seedlings may be due to nothing more than the 
formation of three seed-leaf primordia instead of the normal number, such as 
obtains in many seedlings of Dicotyledons, e. g. Anemone sp. and Salicornia 
herbacea ; further, we have drawn attention to the fact that some subsidiary 
seed-leaves may be due to the displacement of leaves from the first foliage 
whorl to the cotyledonary node, as in Cedrus Deodara and Pinus Pinea } 
It may be mentioned here that Tansley and Thomas 2 have arrived at 
similar conclusions. 
As regards the reasons for this multiplicity of seed-leaves, Masters 3 
has stated his opinion that ‘ It is possible that an increased number of 
cotyledons might, under certain circumstances, be advantageous by securing 
a larger surface and a better chance in the competition with the neighbour- 
ing herbage \ Avebury 4 has suggested that the reason for the deeply bifid 
cotyledons in several plants, e. g. Schizopetalon Walkeri , and Opuntia 
basilaris , is to enable them to be withdrawn more easily from the seed, and 
he asks the question ‘ Is it possible that the multiplicity of the cotyledons 
in Conifers can be due to the same cause ? ’ 
In all cases we have found the mesophyll of the cotyledons to be 
homogeneous in structure, and the parenchyma never shows the internal 
shelves or flanges which is so characteristic a feature in the chlorenchyma 
of the foliage leaves of so many Gymnosperms ; thus the available surface 
in the seed-leaves for the exposure of the chloroplasts is more limited than 
is often the case in the foliage leaves. We therefore think that it is not 
altogether improbable that the longitudinal fission of the cotyledons is 
a means to obtain a greater surface ; for these structures persist relatively 
for a long time, and are thus important contributors to the synthetic food- 
material of the young plant. 
1 Cf. Dangeard, loc. cit. 
3 Masters, 1891, loc. cit. 
2 Brit. Assoc. York. Sect. K, 1906, 
4 On Seedlings, p. 52. 
