INCOMPLETE. 349 



sperm-cells, is the plumule, bearing the whorl of leaves separated by a 

 short internode from the second pair. In the highly developed state of 

 the plumule they resemble Nelumbium. They are found in ditches, &c. 

 throughout the northern hemisphere, and they have no active properties. 



CALLITRICHACEJE are small aquatic annuals, with opposite entire 

 leaves, and solitary polygamous axillary flowers, without any proper 

 floral envelopes ; stamens 1 or 2 ; fruit 4-lobed, 4-celled, 4-seeded ; seeds 

 pendulous ; embryo inverted in the axis of fleshy perisperm ; radicle very 

 long, superior. This Order consists of the genus Callitriche, comprehend- 

 ing the Starworts of our freshwater pools, of which G species occur in 

 Europe and North America. Their flowers are so simple that it is difficult 

 to settle their affinities. Some regard them as related to Hippuris, among 

 the Haloragaceae ; but they appear to be truly achlamydeous, whence 

 others consider them allied to Euphorbiaceee, from which they differ only 

 in their 4-lobed ovary and in the structure of the seed. They have no 

 known properties. 



PODOSTEMACEJE are aquatics, growing on stones in fresh running 

 water, with much the aspect of Seaweeds or Mosses ; the minute flowers 

 bursting from a spathe-like involucre ; perianth or of 3 sepals ; stamens 

 1 or many, hypogynous ; ovary free, compound, 2-3-celled, with 2-3 

 stigmas ; ovules numerous ; fruit a many-seeded, ribbed capsule, the pla- 

 centation of which is axile or parietal ; seeds aperispermic, with a straight 

 embryo. This is a group of very curious plants, having a distinctly Dico- 

 tyledonous embryo, but much the habit of the Monocotyledonous Naia- 

 daceae. Lindley regards them as related to Elatinaceae, or possibly to 

 Plantagiuaceae, by way of Littorella. Hydrostachys is diclinous, the other 

 genera perfect. In some of the genera there is no real distinction between 

 stem and leaf, the structure being analogous to a thallus. They are most 

 numerous in South America ; some occur in India; one in North Ame- 

 rica. They have no active properties ; but some species of Lacis are used 

 for food on the Rio Negro and other parts of South America. 



Series 2. INFERS or 



Ovary inferior. Perianth more or less distinct in the male or 

 female flowers, or both, sometimes none or very indistinct. 



JUGLANDACE^E. THE WALNUT ORDER. 

 Coh. Quernales, Hook. 



Diagnosis. Trees with alternate pinnate leaves, without stipules : the 

 sterile' flowers in catkins, with a simple scale or an irregular perianth; 

 the fertile solitary, or in small clusters, with a regular 3-5-lobed perianth 

 adhering to the incompletely 2-4-celled ovary, with only 1 erect ovule. 

 Fruit consisting of a dehiscent husk enclosing a woody shell, containing 

 a large 2-4-lobed orthotropous, aperispermic seed; cotyledons oily, 



