Facts relating to the Structure of Seedlings. 265 
epigeal seedlings 1 — there is formed either a special structure for its removal, 
as the sucker in Welwitschia and Gnetum , or else the cotyledons are per- 
manently hypogeal and perform the function of absorbing organs. This 
in the case of albuminous seeds : in examples of exalbuminous seeds the 
cotyledons may be hypogeal or epigeal, in which case the hypocotyl forms 
a more or less massive column. The larger the amount of food material, 
the greater must be the vascular supply if the translocation is to be com- 
pleted in a reasonable amount of time. For, although a certain amount of 
water is taken up by a germinating seed through the seed-coat, it is reason- 
able to assume that the larger amount of water is supplied by the root- 
system when once it is formed. And with regard to the depletion of the 
hydrolysed food substances, the phloem, when differentiated, probably is 
more active than the parenchymatous elements. 
Leaving out of consideration those plants, e. g. certain Gnetales, which 
have developed a special structure for this work, the Cycads have in their 
seeds the largest amount of food reserves ; the number of cotyledonary 
bundles are also most numerous in this class. A further example is seen in 
Araucaria ; A. brasiliensis as compared with A. Cunninghamii has a much 
larger seed, its cotyledons are more massive, are hypogeal, and contain 
more vascular bundles, and the hypocotyl is relatively much thicker. 
In such cases we believe that the size of the seed, which presumably 
to a great extent is correlated with the amount of reserve food material, is 
the determining factor, and on it depends the size and number of the 
vascular bundles in the cotyledon, and thus is influenced the transition 
phenomena and the number of bundles and relative development of the 
hypocotyl. 
With regard to the points here raised, although they are now being 
investigated, no information has so far been obtained, other than morpho- 
logical, which warrants our idea that the number and more particularly the 
size of the bundles depend upon the amount of reserve food to be 
hydrolysed and translocated. Thus in the hypogeal seedling of the oak 
the area of the cross-sections of the vascular bundles in the base of the 
seed-leaves of the seedling, plotted against the weight of the seed, minus its 
seed-coat, before germination, gives a very irregular curve. 
The problem, however, is not quite so simple as it appears, since the 
area of the cross-section of the bundles may not bear a definite relation to 
the similar measurements of the tracheae ; the phloem must be taken into 
consideration, and also the capacity of the sieve-tubes ; further, with regard 
to the weight of the seed, it must be ascertained whether it bears any 
relation to the amount of food substances it contains. For instance, it does 
not necessarily follow that the relation between the weights of the food 
1 Reed, T. : Some Points in the Morphology and Physiology of Fasciated Seedlings. Ann. 
Bot., 1912, xxvi. 
