i6 BOTANY AND PHARMACOGNOSY. 



made up of the valves of diatoms, is used chiefly as an absorbent 

 agent for storing nitroglycerin, as in the production of dynamite. 

 Being a non-conductor of heat the material also finds use in the 

 manufacture of the so-called isolation plates for machinery. 

 Another use is as a tooth powder. Among the Chinese and Lap- 

 landers diatomaceous earth has also been used as an edible earth 

 known as " mountain meal " or " bread-stone." It has been used 

 in India as a rubefacient. 



Many of the Algae are of use as food, of which the following 

 may be mentioned : Vaucheria fastigiata, Griffitlisia coralina, 

 Ceramiuiii Loureirii, Chondrus crispns (Fig. 9), Gigartiua mamil- 

 losa(Fig.2y8a.), Gclidiuni cartilagineurn, Gelidiitm crinalc (yield- 

 ing agar-agar), Rhodymcnia pahnata (yielding dulse), and sev- 

 eral species of Gracilaria (which also yield agar-agar). 



Some of the sea-weeds are used in the production of iodine, 

 as DiirviUcra utilis, AscopliyUnm nodosum, Fucus vcsicidosns 

 (bladder-wrack), Sargassiiiii liiiifolliiui. Laminaria saccharina, 

 Laiiiinaria digitata, Alaria csculcnta, Rhodyiiicnia pahnata, Phyl- 

 lophora mcmhranifolia, Macrocystis pyrifcra, and Fastigiaria fiir- 

 ccllata. 



A number of the Algae are also used in medicine, particularly 

 for phthisis, as Fiicns cartilaginctts, StUophora rhicodcs and 

 Dictyoptcris polypodioidcs. Alaria csculcnta and Laminaria digi- 

 tata are used in the making of bougies and tents used in surgery. 

 Owing to the toughness of some of the Algae on drying, the 

 material is used in the manufacture of various articles, as handles 

 for tools from the thick stem of Lcssonia fnccsccns, fishing lines 

 from Chordaria filum, etc. 



FUNGI. 



The Fungi form a large group of plants which do not produce 

 chloroplasts or any bodies having a similar function. Thev have 

 not the power of carbon dioxide assimilation, that is, unlike the 

 Algae they are unable to manufacture food materials, such as 

 carbohydrates (starches, sugars, etc.), from carbon dioxide and 

 water. Hence they are dependent upon previously formed food 

 products, and may derive their food from living plants or ani- 

 mals, when they are known as parasites, or from decaying animal 



