238 mr. s. le m. moore's studies 



Some Remarks on the Function of Callus and Paracallw. 



In the former memoir I adopted Sachs's view that the function 

 of callus is to act as a mechanical hindrance to the flow of proteid 

 &c. along the sieve-tubes. I do not know to what length Sachs 

 would carry this idea, neither am I aware of any attempt to think 

 out fully the effects which one would expect to occur were the 

 sieve-plates not blocked up in winter with callus or paracallus, 

 or some other substance with a similar function. Let us sup- 

 pose the flow along the sieve-tubes to be absolutely without 

 hindrance ; how, then, could our arborescent vegetation survive? 

 In these latitudes scarcely a winter passes without some days 

 of premature warmth, during several hours of which the mercury 

 rises far above the minimum point, and sometimes stands not 

 very much below the optimum temperature for growth. Under 

 these circumstances a certain amount of activity manifests itself 

 at the vegetative points : leaf-scales elongate, and may betray a 

 tendency towards epinasty, thus partially exposing the tender 

 young leaves ; and should the weather continue warm, the infant 

 axes may begin to lengthen only to be destroyed with the re- 

 currence of seasonable weather. Now if this can happen when 

 the growing-points are shut off from access to the stores of 

 proteid and carbohydrate pabulum accumulated in them, what 

 would be the upshot if these stores were not safely locked up ? 

 Were this the case, we may be sure that a fortnight's warm 

 weather in winter would witness an astonishing advance — growing 

 axes would elongate, leaves would stretch and unroll, probably 

 many flowers would expand ; and all the energy used up over 

 this would be so much dead loss to the plant, and worse than 

 dead loss, because more energy would have to be drawn upon 

 for the production of new meristematic points to replace those 

 cut off. A healthy tree would doubtless respond to the call upon 

 it, and during its first season, under the altered conditions, would 

 show but faint signs of a change in the order of nature. Its 

 store of accumulated energy would, however, be less during the 

 following than it was the preceding winter ; and this diminu- 

 tion would, irrespective of the loss from precocious sprouting, 

 betray itself next year in the production of fewer and probably 

 of smaller leaves. In fact, cur supposed tree would be m the 

 position of a person living to some extent upon his capital. \> e 



