2io Takcda. — Some Points in the Morphology of the 
double stipules may be produced in the region in which the number of 
‘ leaves 5 is undergoing increase, or on the other hand reduction from node 
to node. It is evident that at the base of a seedling a double stipule repre- 
sents a stage of progression, while towards the apex of a stem it usually 
represents a stage of retrogression. It has already been pointed out that in 
the Stellatae the four-membered whorl seems to represent within the limit 
of possibility the most primitive type. Hence it follows that the progression 
generally speaking would have been from the four-membered whorls to those 
with six or more members by fission of the original two stipules. In the 
case of any ‘ four-leaved ’ species, such as Galium gracile , the occurrence of 
double stipules therefore indicates a step towards the production of ‘ five- 
leaved ’ species. 
A case presenting some phenomena similar to those described above 
(though not involving stipules) has been recorded by Groom , 1 who found in 
Lysimachia vulgaris that dimerous nodes occurred at the base, tri- to 
tetramerous nodes higher up on the stem, and finally in the uppermost 
region of the stem dimerous nodes reappeared. In this case the transition 
was often accomplished by one or two double leaves at intermediate nodes. 
The same author 2 found in Rhinanthus Crista-galli that a double leaf stood 
at the transitional region from cyclic arrangement of leaves to acyclic. It 
appears certain that in the former case (i. e. Lysimachia ) the double leaves 
represent on the whole in the lower region of the stem a stage of pro- 
gression, and in the upper region one of retrogression. In the latter case 
(i.e. Rhinanthus) the double leaf doubtless represents a stage in the complete 
replacement of two opposite leaves by a solitary leaf, by means of a con- 
crescence . 3 
In dealing with double stipules (and double leaves), it should be borne 
in mind that the foliar organs of this nature may sometimes be produced 
without relation to the general tendency of arrangement and distribution of 
‘ leaves ’ in the stem. Some of the cases above described may again be 
referred to. In the case of Galium leiophyllum a four-membered whorl near 
the base of a stem is succeeded by a five-membered whorl, thus showing 
a tendency of increase in the number of ‘ leaves ’. At the next node the 
whorl is again four-membered, but one of the two stipules has tvyo midribs 
(Fig. 21), apparently indicating a transition towards decrease in number. 
The next whorl is however again five-membered, and all the nodes (about 
four have so far developed) succeeding this particular one are six-membered. 
In the examples of Asperula trifida , which have been described above in 
detail, the number of members at succeeding nodes does not show a regular 
1 Longitudinal Symmetry in Phanerogamia. Phil. Trans. Roy. Soc. Lond., B, vol. cc (1908), 
p. 84 et seq. 
2 Groom, 1 . c., p. 106. 
3 For further instances of similar phenomena see Worsdell, Principles of Plant-Teratology, 
vol. i (1915), p. 216 et seq. 
