Chap, i.] by Malpighi and Grew. 237 



much misinterpretation and to gross errors on the part of latei 

 writers. Malpighi thought he observed a peristaltic movement 

 in these vessels, a delusion to which many of the nature- 

 philosophers were particularly fond of surrendering themselves 

 at the beginning of the present century. 



In addition to the bundles of fibres and the tracheae, Mal- 

 pighi observed a number of tubes in Ficus, Cupressus, and 

 other plants, which allowed the escape of a milky juice, and 

 he concludes that similar special tubes might be present also 

 in the wood of stems from which milk, turpentine, gum, and 

 the like exude. 



Such are the elementary organs of plants, as far as they were 

 known to Malpighi ; in the subsequent part of his book we 

 find them applied to a histology of the stem, and here a mistake 

 at once makes its appearance, which, resting on his authority, 

 was reproduced by the phytotomists of the 18th and even of 

 the early part of the 19th century, — the theory, namely, that 

 the young layers of wood in the stem originate in the periodic- 

 transformation of the innermost layers of bark (secondary 

 bast-layers) ; Malpighi was led into this mistake, as it appears, 

 partly by the softness and light colour of the alburnum, partly 

 by its fibrous character. In this substance the spiral tubes are 

 gradually formed, and as the mass becomes more solid and 

 compact, it subsequently forms the true wood. 



The pith lies in the centre of the stem, and, according to 

 Malpighi, consists of numerous rows of spheres (' multiplied 

 globulorum ordine ') arranged longitudinally one after another, 

 and composed of membranous tubes, as may be clearly seen 

 in walnut, elder, and other trees. In this place also he men 

 tions the milk-vessels in the pith of the elder. Passing over 

 many and various matters, it may be mentioned next that 

 Malpighi recognises the connection of the layers of tissue in 

 young shoots with those of the parent-stem, and very expressly 

 notices the same continuity of structure between the leaf and 

 the axis of the shoot. He then briefly touches on the anato- 



