6 Miss Robertson, Notes on the Anatomy of 



and giving it out to the surrounding tissues in times of scarcity. 

 In describing Encephalartos Gaffer, Worsdell 1 puts forward the 

 following elaboration of Vetters' theory: — "It appears that these 

 plants, which grow in clefts of rocks in the hilly country of South 

 Africa, have, at a certain season of the year, to endure a dry 

 season, during which their tap-root entirely dies away, along with, 

 presumably, the foliage. During this period the stem, swollen as 

 it is with its massive parenchymatous tissues and protected 

 externally by the thick and coriaceous leaf-bases, probably acts as 

 a water-reservoir by means of the network of mucilage canals 

 penetrating every part of the organ, the mucilaginous secretion 

 serving to retain every particle of moisture previously absorbed 

 by the root, and thus to preserve the stem from desiccation." 

 Worsdell points out in connection with this theory that the roots 

 are entirely devoid of mucilage canals. 



It has occurred to me that it is just possible that this great 

 accumulation of mucilage may serve another purpose, besides 

 being an adaptation to a xerophytic mode of life. Mucilages 

 seem in general to have the same percentage composition as 

 cellulose, and the gap between typical cellulose and mucilage is 

 bridged by the " hemicellu loses" which often form the reserve 

 material in seeds. Cases are known in which gummy substances 

 serve as a store of food, for example the mucilage dissolved in the 

 cells of Orchid-tubers and the rhizomes of Symphytum 2 , and 

 according to Haberlandt 3 , the "Schleim" of the endosperms of 

 various Leguminosae. It is generally assumed that the mucila- 

 ginous substances stored in the canals of Cycads, and other 

 similar receptacles, take no further part in the metabolism of the 

 plant ; but is it not possible that they form a reserve of food 

 material which may be drawn upon in case of special need ? The 

 development of the large reproductive organs of a Cycad is a very 

 rapid process compared with the slow vegetative growth of the 

 same plant, and must mean a great drain upon its resources. If 

 the accepted view is correct, the plant has locked up irretrievably 

 an abundant store of organic substance in its mucilage canals, 

 and in times of need it might starve within sight of plenty. The 

 curious fact that the bundles Avhich arise in the pith in connection 

 with the mucilage canals seem invariably to orientate themselves 

 without regard to anything but the position of the canals, may 

 perhaps receive its explanation if the canals are really store- 

 houses of food material; for the phloem is invariably turned 

 towards the accompanying duct. On the other hand the possi- 

 bility of an entirely opposite explanation must be remembered, 



1 Trans. Linn. Soc. Vol. v. 1900, Part xiv. p. 448. 



2 Pfeffer's Physiology of Plants, Vol. i. Trans, by Ewart, 1900, p. 478. 



3 Physiologlsclie Pjlanzen-Anatomie, 1896, p. 36. 



