06 TOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



during the earlier stages of growth, as the roots penetrate the surface 

 layers of soil only. By a glance at the figure given, the " superficial root 

 svstem " is aptly shown from nature in a vertical section, and may be 

 readily understood. Some considerable period must therefore elapse 

 before they can reach the level of "permanent moisture." 



And thus, dm-ing the earlier stages of growth, anything which tends 

 to shade the soil and preserve moisture is an indirect factor in the 

 economy of the plant. For this purpose suitable "catch crops" of 

 a leguminous nature as the Pigeon-pea, Cajanus iJidicus, may be 

 used. They would thus answer the combined purposes of shading and 

 conserving moisture in surface layers of soil, keeping down weeds, and 

 adding to the nitrogen in the soil in a similar manner to our own clovers. 

 An occasional row of suitable trees may often be used advantageously as a 

 wind-break. For this purpose Bananas, together with various forest trees, 

 are used in several districts of Porto Rico and Mexico. 



Finally, a list of shade trees and catch crops grown in conjunction 

 with coffee in the various regions of cultivation, giving both common and 

 botanical names, with brief descriptive notes, is well worthy of perusal 

 by either present or prospective planters. — E. F. H. 



Cycas Tubercles. 



Cycas, Tuber-like Rootlets of. By A. C. Life {Bot. Gaz. vol. xxxi. 

 p. 205, No. 4 ; with 10 tigs.), — The anatomical structure of the so-called 

 tubercles which appear to be fundamentally of a root-like nature, pro- 

 jecting from near the apex of tree-roots and branching dichotomously. 

 They contain a zone nearly midway in the cortex of longish cells associated 

 with intercellular spaces. It appears that fungi, such as bacteria and 

 mycelium, prepare the way for an alga, by causing destruction of cells 

 and the production of empty spaces. The alga, which appears to 

 resemble the green chain of cells in the lichen Xostoc, takes up its abode 

 in the intercellular spaces, giving a greenish colour to the zone. This is 

 interrupted at places below lenticels, so that the author comes to the con- 

 clusion that those tubercles of Cycads may be said to have at least two 

 functions, that of aerating and that of assisting in nitrogen assimilation 

 the alga li^•ing in symbiotic association with the Cycad. — G. H. 



Cryptogamic Diseases. 



Diseases of Plants, Cryptogamic. By J. Piay (Bev. geu. Bot. 

 xiii. p. 145, 1901). — Many parasites are superficial and only affect the host 

 plant locally. Thus Botrytis cinerea is said to develop on the green 

 leaves and flowers of many plants, and to injure them indirecth' by inter- 

 fering with respiration and carbon assimilation. The eWls can be 

 remedied by exposing to a light sufficiently intense to permit the 

 chlorophyll to resume its activity in spite of the covering of mould. The 

 oxygen, it is said, may be also administered in the form of injection of 

 oxygenated water. But the author does not suggest that these cures 

 l^ossess more than a theoretical interest. 



When dealing with internal parasites, e.g. Botrytis, as it often 



