Decembeb 15, 1888.] 



THE GARDENERS' CHRONICLE. 



697 



gathered and dried out in South Africa to use among 

 clothes and lines as Woodruffe is in some parts of 

 Europe. Most of the other Satyri urns are also very 

 fragrant when in bloom. James O'Brien. 



Via. 98. — SATYBIUM CARNEUM : FLOWERS PALE PINK, BRACTS BEOWNISH, 



THE CHEMISTRY OF VEGETA- 

 TION, IN REFERENCE TO THE 

 GROWTH OP THE POTATO. 



(Conclwlul from p. 633.) 

 Growing under Control. — This question may 

 perhaps be put: — Supposing we did know with 

 exactness all the conditions under which a tuber is 

 formed, and the limits of the variations which may 

 be reached without materially affecting results, 

 and did know the extent to which its forma- 

 tion, chemical composition, and period of maturing 

 could be controlled, if the Potato were grown in 

 houses where not only soil, temperature, and moisture 

 of air, but also the colour and over intensity of the 

 light could be arranged, how could all this knowledge 

 help the cultivator who grows by the acre in the 

 open, where his crop is exposed to climatal condi- 

 tions which are so variable and so different in their 

 variability from year to year, and so much beyond 

 control ? With our present partial knowledge, or, 

 more correctly, want of knowledge, a complete 

 answer to such a question cannot be given. We do 

 not yet know enough of conditions and of results of 

 conditions to know what we might do, but some few 

 suggestions may be given that may help eventually 

 to answer the question. 



It is a well established fact plants do acquire 

 " habit," that " habit " is transmissible by seeds or 

 cuttings, and that it may become intensified in 

 successive years. This intensifying in the case of pro- 

 pagation by seeds appears to depend on a less direct 

 connection with the parent plant than in the case of 

 cuttings; but as likeness of the offspring to the 

 parent (with probabilities of " sport," which seem about 

 equal in either cases) comes about from both means 

 of propagation, the difference is probably more 

 apparent than real. Be this as it may, a newly- 

 acquired " habit," it seems, is sometimes inherited, 

 and if the conditions that started it remain natur- 

 ally, or are by art made to remain the same, the 

 habit is intensified. In the ease of dicecious plants, 

 and of artificial cross-fertilisation, there are two 

 factors to consider in seed-propation ; in moncecioi'8 

 plants and with cuttings, only one. In Potato 

 growth, propagation by cuttings is the rule (as the 

 tubers are but underground stems), artificial cross- 

 fertilisation, to endeavour to produce a new " variety," 

 quite the exception. But, judging by analogy from 

 other plants, " habit" in the Potato might be inten- 

 sified by either method of propagation. Potatos are, 

 as a rule, grown in such a haphazard way, and without 

 any record of observations, that there seem no data 

 for knowing what the limits of this intensifying are. 

 Direct experiments continued over a series of years 

 would decide this with at least some certainty. 



Now, we have seen the way in which our modern 

 theories of chemistry have influenced the investiga- 

 tion as to how starch is first formed in plants — that 

 is, in plants generally. There have been no direct 

 observations on the Potato so far as I can find, but 

 there is no reason for supposing it offers any excep- 

 tion to the rule. The "reserve material" of a seed 

 starts a young plant if grown from seed, of a stem 

 if grown from a cutting (from a swollen stem in the 

 case of the Potato). Then when the independent plant 

 has grown far enough to " feed " itself it forms starch 

 by decomposing carbonic acid and water. But only 

 under certain conditions. The surface of the leaf must 

 be moist ; and light waves of certain lengths only 

 and of certain combined " intensity " can effect this 

 decomposition. 



We need not trouble for practical purposes much 

 about Pringsheim's hypochlorin. Sachs has re- 

 peatedly asserted and re-affirmed that starch is the 

 first visible product formed. Pringsheim says hypo- 

 chlorine precedes it. As a scientific study the subject 

 is of interest, but practically both agree in this, that 



