452 
Hill and de Fraine . — On the 
goes on to remark that ‘ it might be assumed that the median bundle, when 
present, is merely the result of the coalescence of two equal bundles, which 
might be found to be distinct in the upper part of the cotyledon ; but this 
is not the case, since the median bundle has been found to maintain its 
individuality in an upward direction \ 
Further, Miss Thomas and Tansley found that Cycas revoluta had 
a tetrarch root, whereas Van Tieghem 1 describes it as being diarch, and 
Worsdell 2 as triarch or tetrarch. 
Finally, as regards the number of bundles in the cotyledons, Worsdell 
describes those of Cycas revoluta as having five strands in the apical parts, 
which at lower levels fuse together so that three enter the axis. 
Ceratozamia. 
Ceratozamia mexicana , Brongn. is of particular interest, owing to the 
presence of one seed-leaf only, the other being frequently aborted. Our 
knowledge of the seedling structure of this plant is practically complete, and 
is due to the researches of Miss Dorety 3 and Matte . 4 Considering the 
work of the former author first, the cotyledon, which in many cases is lobed 
at the tip, has many bundles in its distal region which increase in number 
towards the base and then undergo a reduction in number so that, finally, 
three strands only enter the axis. Reading the serial sections in the 
opposite direction three traces enter the seed-leaf from the hypocotyl, and 
each dichotomizes several times, hence, in the upper parts, the number of 
bundles may be fifteen, which undergo reduction as the apex is reached. 
The three traces each behave in the same manner, ‘ the median one being 
no more a “ double ” bundle than any of the others.’ The transition takes 
place rapidly, each cotyledonary strand giving rise to one pole of the root- 
structure, which is either triarch or tetrarch ; whether the vascular arrange- 
ment of the root be triarch or tetrarch seemingly depends upon the degree of 
development attained by the median bundle of the aborted cotyledon. 
When the second seed-leaf is made to develop, the transition-phenomena 
closely resemble those described for Dioon edule by Matte 5 and Thiessen 6 ; 
three strands enter the axis from each seed-leaf, one central and two lateral, 
the two central ones organize those two poles of the tetrarch root-structure 
situated in the cotyledonary plane, and the corresponding, i. e. opposite, 
lateral strands of the seed-leaves fuse together and form the two poles in the 
intercotyledonary plane. 
Turning to the results obtained by Matte, who enters very fully into 
the anatomy and morphology of seedlings of different ages, it is clear that 
1 loc. cit. 2 loc. cit. 
3 Dorety : The Embryo of Ceratozamia , a physiological study (Bot. Gaz., xlv, 1908). 
The Seedling of Ceratozamia (Bot. Gaz., xlvi, 1908). 
4 loc. cit., 1908. 5 loc. cit., 1904. 
6 loc. cit. 
