Stipules in the Stellatae , with special reference to Galium . 21 1 
sequence, but repetition of increase and decrease may be seen. In such 
cases, double stipules may be clearly associated with either increase or 
decrease, or sometimes a decision on the subject may be impossible . 1 At 
the same time it may be noticed in many cases that in alternate nodes the 
number of the f leaves ’ and also the nature of the stipules are more closely 
correlated than in successive ones. 
Explanations may be sought for partly in some physiological factors 
which either promote or retard the growth of a plant. Boodle 2 found in the 
seedlings of the gorse that similar irregularities often occurred regarding the 
distribution of the trifoliate leaves. He is of opinion that this is at any 
rate partly due to variation in some physiological conditions during the 
growth of the seedlings. On the other hand, Groom’s suggestion 3 regarding 
a similar phenomenon exhibited by Lysimachia vulgaris , that ‘ morpho- 
genous impulses are transmitted along the orthostichies may give the 
explanation of the alternating number of members at succeeding nodes 
described in some of the above examples. 
Turning to the case of a seven- or eight-membered whorl, it may be 
held that the middle stipule of the three (on one or both sides of the node) 
has originated by fission from one of the two adjoining stipules. Since the 
middle stipule usually takes exactly the median position and assumes the 
same size as the others, its relationship to the one or the other of the two 
adjoining stipular members cannot be determined. This occurrence may 
conveniently be termed a congenital fission (chorisis, dedoublement) in con- 
trast with the phenomenon known as congenital fusion. If this congenital 
fission once starts in any species it may be repeated more than once, 
resulting in the production of as many stipules as space will permit on 
either side of the node. Hence, we more often find the pleiomerous whorls 
in the species with narrow ‘ leaves ’ and a comparatively thick stem, such as 
Galium verum. 
In the case of the pleiomerous whorls, stipules are known to occur as 
many as five on either side, and they probably develop from as many 
primordia as there are stipules, without showing any connexion with one 
another. 
A parallel case may be found at the cotyledonary node in many of the 
Conifers and a few Dicotyledons, in which the two original cotyledons have 
undergone chorisis, thus giving rise to a polycotyledonous condition. In 
these cases the increase in the number takes place as a rule without any 
transitional stages, and double cotyledons are not frequently in evidence. 
The double cotyledons recorded by Groom 4 for Acer P seudoplatanus 5 and 
1 Cf. Worsdell, 1 . c., p. 238. 
2 On the Trifoliate and other Leaves of the Gorse (UZex europaea, L.). Ann. Bot., vol. xxviii, 
(193:4), p. 527 et seq. 
s Groom, 1 . c., p. 86. 4 1 . c., pp. 102-3. 
5 Also see Worsdell, he., p. 215, FI. XIX, Fig. 4 a. 
