2 22 INTERCELLULAR SPACES. 



their vertical branches is often much greater than in the above, reaching not un- 

 commonly 1 80^, so that the hair appears in profile in the form of a letter H. 



In the lacunar of the lamina the form of the hairs in the portion near the lower 

 surface does not differ essentially from that above described. At the limit be- 

 tween this and the lamellar layer of parenchyma of the upper surface are found 

 numerous hairs, which put out diverging arms both downwards into the lacunae, and 

 also upwards : these run straight and perpendicular between the lamellae of paren- 

 chvma, as far as the inner surface of the epidermis ^. 



In the air-passages of those Nympha^aceae which have been investigated, at 

 least in those of the petiole, there occurs another sort of hair formation, different from 

 that described. Single cells of the lateral wall put out into the passage a sac-like 

 outgrowth, which branches frequently and irregularly to form many arms, and is 

 divided by septa into cells, which are also irregular and many-armed. The same 

 p-rowth continues in these for a long time, so that a small lacunar mass of cells is 

 formed, which loosely fills up the passage like a diaphragm of many layers of cells. 

 The cells of these pseudo-diaphragms have permanently delicate, smooth walls, and 

 scanty protoplasm with some few starch-grains ^ 



Hard stellate hairs with pointed arms, resembling closely those of the Nymphae- 

 acece, are found in the air-passages of Limnanthemum nymphoides, and other 

 investigated species of the same genus, in stems, rhizomes, and petioles''. They are 

 always distinguished from those of the Nymphceacese by their smooth membranes; 

 many protrude only into a single air-passage. These stellate hairs have not hitherto 

 been found either in the true Villarsias, or in other Menyantheae, or in other water- 

 plants of like habit. 



In certain Aroideai, viz. the group of the Monsterinea? (Monstera, Tornelia, 

 Heteropsis, &c.), Pothos Rumphii, and Spathiphyllum*, numerous hairs of this sort 

 are contained in the cavities and passages of the lamellar parenchyma. They usually 

 occur in all parts of the plant, or they are absent in certain parts, e.g. the rhizome 

 and the roots of Spathiphyllum. They arise by early outgrowth of a cell of the wall 

 of the cavity (usually one layer of cells thick) which remains relatively narrow, so as 

 to form long, thin pointed arms. In the longitudinally elongated cavities of inter- 

 nodes, petioles, and roots more simple forms occur as a rule : each hair-cell grows 

 out into one, two, or rarely three of the adjoining passages, forming in each two arms 

 of equal or unequal length, and tapering very gradually to a point : these diverge 

 exactly 180° from their point of origin. The hair thus assumes the form of a spindle- 

 shaped body, with a short blunt transverse appendage, which is fastened in the 

 lateral wall of a cavity : or of an H with a short transverse portion, which is im- 

 bedded in the lateral wall between two cavities (Fig. 89). Of the many irregularities 

 which occur in this type, only one need be mentioned here, viz. that an arm may put 

 out single lateral branches, which enter like hooks into neighbouring lacunae. In the 



1 Meyen, ITaarlemer Preisschr. Taf. V; Physiol. /. c. p. 312. — Trecul. /. r. pi. 12, fig. 25. 



2 Trecul, /.c. fig. 12.— Frank, /.c. p. 153. 



* Grisebach und Hoffmann, Linncea, Bd. XII. p. 6S1.— S. F. Hoffmann, Ibid. Bd. XIII. p. 291 



* Van Tieghem, Structure des AroidJes, /. c. p. 137, &c. 



