434 MORPHOLOGY. 



cells with spiral and reticulated layers of thickening, as, for instance, in the 

 LabiatcB (especially Salvice), and in the Casuarinacece ; and the hairs of 

 the epidermis often exhibit the same, as in some Composite (Senecio and 

 Trichocline\ &c. The most beautiful structures of fibrous cells are 

 formed through the entire tissue of the indehiscent germen, as in the 

 Composites (Picridium) and the Umbelliferce ( Sclerosciadium Prangos). 



174. Similar conditions to those which occur in the bursting of 

 the anthers and in the fall of the leaves are also presented in the 

 fruit, and depend on the same causes, namely, the formation of 

 layers of cellular tissue extremely thin-walled and easily destruc- 

 tible, which is ruptured by the slightest tension arising from the 

 mere weight of the parts, or an unequal contraction of dissimilar 

 layers of cellular tissue. This exists either as a peculiar layer 

 between two differently formed masses of cellular tissue, or forms 

 the external layer of a mass of tissue, itself having thin walls, and 

 lying immediately in contact with some very thick- walled tissue. 

 Whether separations of this kind shall take place, and in what par- 

 ticular situations, are altogether peculiarities of particular species, 

 genera, and families, and are not dependant on any known relation 

 to the nature of the" plant. Hence solutions of continuity arise, 

 sometimes at the place where two originally separate parts (carpels) 

 had become blended in the suture, or else where an undivided whole 

 originally existed *, as in the line corresponding to the mid-rib of a 

 carpel ; sometimes in the direction of the length, as in the examples 

 which have been cited, and sometimes cutting across, as when the 

 entire fruit falls away, or when long fruits break up into separate 

 articulations, &c. ; sometimes only in small portions of the germen, 

 so that it opens by definite orifices. Many fruits are rent open in 

 the most diversified manner by the always unequal drying of the 

 pericarp, on account of the differences of the layers of which it is 

 composed. They may open either, , in individual portions, 

 each closed in itself, and separating either lengthways or crossways 

 (niericarps) ; or, b, in individual flat portions (valves). In the lon- 

 gitudinal division or the formation of valves, there remains besides 

 these parts, in many families, a mass of cellular tissue, usually in the 

 form of a stalk, standing in the midst of the individually separating 

 mericarps, as in the Umbelliferce, the Euphorbiacece, and Geraniacece, 

 or of the separating valves, as in Rhododendron, called the columella. 

 This is merely a separation of originally connected parts, and in 

 none of the cases named is the remaining stalk by any means an 

 internode of the floral axis to which the carpels were attached, but 

 an absolutely independent cellular mass. 



In very many manuals of Botany, we find directions to determine the 

 number of carpels according to the valves of the fruit. How absurd 

 this is, the authors might have known, from the transverse separation 

 of the so-called circumscissile capsule and of the lomentum into separate 



* Here, also, no trouble being felt about the thorough diversity, the line of separa- 

 tion has received the meaningless name of suture. 



