104 
alpinum magis spectans; pedunculus 5—6 cm longus æqua- 
lis; spica 20—30 mm longa floribus sterilibus. 
This hybrid differs from P. alpinus, with which it by 
some authors has been associated, through the leaf-base, 
that usually is somewhat ovate or even slightly cordate, the 
denticulation very passing but on the youngest submersed 
leaves distinct, the eventual ramification and upper floral 
leaves, that never seem to bear well-developed petioles. The 
transverse section of the stem commonly exhibits a thicker 
central cylinder than has P. alpinus. From P. perfoliatus 
it is distinguished through the basis of leaves, the stipules 
and upper more or less broad-petioled leaves; from P. 
gramineus + perfoliatus (P. nitens Web.) by the obtuse apex, 
the much weaker denticulation, the lack of mechanical sy- 
stem in the stem-structure and the endodermis, that always 
consists of 0-cells. 
As all bastards also the present hybrid occurs with 
forms, that either with all or at least with part of then- 
organs are intermediate or more or less approach either of 
the parents. All forms seem to partake in following cha- 
racters. Stem pretty high, internodes 6 — 15 cm long, sub- 
mersed leaves green, elongated with the largest width in 
the middle, apex obtuse, margin faintly serrulate only per- 
ceptible on very- young leaves and by- microscope, upper 
leaves more or less subcoriaceous with sloping base, more 
or less shortly broad-petioled; stipules intermediate soon 
decaying; peduncles short, spikes with more or less abor- 
tive flowerparts. Anatomy is distinguished by- the lack of 
mechanical tissue and an endodermis of 0-cells. 
Two formseries are to be distinguished: 
I. series abbreviata: folia submersa breviora latiora 
basi ± cordato. 
II. series alpim folia: folia submersa pro ratione prioris 
longiora, sæpe 200 mm et ultra, angustiora basi ± rotundato- 
lanceolato (P. alpino similio’re). 
I. ser. abbreviata Hagstr. 
