178 



LECTURE XI. 



Among the Gymnosperms, Welwilschia mirabilis — so very remarkable in other 

 respects also — has thousands of well-developed oxalate crystals contained in the 

 substance of the very thick walls of the schlerenchymatous cells (Fig. 178). 



The quantity or oxalate of lime may occasionally be enormous. According 

 to Schleiden, the dry substance o{ Cereus senilis contains more than 85 per cent, of its 

 weight of it. This substance is also generally abundant in the parenchyma of foliage 

 leaves, as well as in the secondary cortex and pith of dicotyledonous woody plants, and 

 occasionally in the medullary rays also [Camellia, Vitis). Sometimes, however, the 



crystals are entirely wanting, as in the Equi- 

 setaceae, and most Ferns and Grasses; and 

 even in families of Phanerogams which are 

 otherwise rich in calcium oxalate it is absent 

 in single species, e. g. in Petunia nyctaginiflbra 

 (Solanaceae), in Tulipa silvestris, Lilium niar- 

 tagon, and Lilium candidium (De Bary). 



With regard to its distribution in the tissues, 

 we may notice the frequency of crystals of 

 oxalate in rows of cells which accompany 

 the vascular bundles, or run in the secondary 

 cortex, or which, on the other hand, occur in 

 groups or rows beneath the epidermis. Many 

 Monocotyledons are especially remarkable for 

 the serially arranged large vesicles, containing 

 slime and raphides, in the petioles, leaves, 

 and bulb-scales — e. g. the Commelynacese, 

 Amaryllidese, and Palms. 



In many crustaceous Lichens, and to a 

 less extent in some other Fungi, calcium 

 oxalate is excreted in large quantities on the 

 exterior of the cells. Although oxalate of 

 lime is occasionally met with in the form of 

 small crystals suspended in the protoplasm ; 

 in living cells rich in protoplasm, and even 

 in those containing chlorophyll, this does not 

 affect its being a useless secretion, since even 

 in living cells — e. g. in hairs rich in pro- 

 toplasm — such an excretion may obviously result without the life of the cell itself 

 being endangered. 



In comparison with the exceedingly common occurrence of calcium oxalate, the 

 excretion of calcium carbonate in solid masses is rare. Among the Phanerogams 

 there are two families especially — the Urticacese in the wider sense, and the Acan- 

 thaceae — which are remarkable for the presence of so-called Cystoliths ; in the first 

 family in connection with the epidermal system, in the others in the interior of 

 the fundamental tissue. Cystoliths are massive bodies, often resembling a bunch of 

 grapes, attached by a thin short stalk to the wall of the cells in which they are 

 contained. The substance of this body tionsists of cellulose, which is permeated by 



FIG. T78. — Half of a sclerenchyina cell from Welwit- 

 schia mirabilis, with numerous crystals of oxalate of lime 

 einlaedded in the outer layer of the very thick wall. 



