A STUDY OF THE INFLUENCES OF DEFOLIATION AND PINCHING-BACK ON YOUNG MULBERRY TRESS IN THE NURSERY : II. The INFLUENCES OF PINCHING-BACK

1) We have made an enquiry into the effects of \u22pinching-back\u22 on young mulberry trees in the nursery, as practised in various stages of their growth. For the purpose of comparative study, we divided our nursery into the following sections:? The \u22Control\u22 Section, where no pinching-back has been practised. Section \u22A,\u22 where the trees were pinched back once in late September while in growth. Section \u22 B,\u22 where the trees were pinched back once in August, and then the axillary buds sprouting thereafter were all removed. The growth of stems having thus been checked, the leaves borne by these trees have been much limited in number. Section \u22C,\u22 where the trees were pinched hack once in August, and then only two or three uppermost axillary buds were allowed to grow from each tree. In autumn, the leaves borne by these new stems were collected for September-silkworm-culture. 2) The trees in Section \u22A,\u22 where the pinching-back was practised in autumn, are generally found to be compared favourably with those in the \u22Control\u22 Section, in the gross weighte respectively of the young trees, the roots, and the stems; in the length of the stems, and in the weight of the stems cut to a certain uniform length; in the diameters of the transverse sections of the stems; etc. On the other hand, the trees in both Sections \u22B\u22 and \u22C\u22 are found to be inferior in all these respects to those in the \u22Control\u22 Section; while the ratio between the diameter of the pith and that of the stem is found to be large in either of these Sections to the same ratio in the \u22Control\u22 Section. 3) The trees in Section \u22A,\u22 while in the breaking strength and the specific gravity of the stems approximately resembling those in the \u22Control\u22 Section, have had smaller parts winterkilled. On the other hand, the tree s in Section \u22B,\u22 though having a somewhat smaller breaking strength and smaller specific gravity of the stems, have been least susceptible to winterkilling. Lastly, Section \u22C\u22 has presented the poorest results, having the smallest breaking strength and specific gravity of the stems, and having had the largest parts winterkilled. 4) As compared with the \u22Control\u22 Section, Section \u22A\u22 has been observed to contain almost equal percentages respectively of water, dry matter, ash, and organic matter; whilst Sections \u22B\u22 and \u22C\u22 generally contain larger percentages of water and ash and smaller percentages of dry and organic matters. 5) As compared with the \u22Control\u22 Section, Section \u22A\u22 contains a more or less smaller percentage of soluble carbohydrates; especially is this the case with the preserved carbohydrates contained in the roots, the proportion of such preserved nutriments markedly tending to be inferior in the trees in this Section. Sections \u22B\u22 and \u22C\u22 are both inferior to the \u22Control\u22 Section in the proportional quantities of the above mentioned constituents, particularly so as regards the preserved carbohydrates contained in the roots. This general tendency in the \u22treated\u22 Sections may be attributed to the comparative scarcity of foliage resultant from the pinching-back and disbudding. 6) As regards nitrogen compounds, little or no marked difference is noticeable among the four Sections studied: only, Section \u22B\u22 tends to hold a larger percentage than other Sections of these compounds. Thus, it has been observed that the percent ages of the nitrogen compounds contained in the trees in the four Sections present somewhat different aspects from the percentages of the soluble carbohydrates contained in the same. 7) As regards these constituents and preserved nutrinents contained in the roots and stems, Section \u22A\u22 generally resembles the \u22Control\u22 Section, in the absolute quantities of the dry matter, of the ash, and of the organic matter, but tends to be somewhat inferior in the absolute quantities of the soluble carbohydrates and of the nitrogen compounds. Section \u22B\u22 and \u22C\u22 are both inferior to the \u22Control\u22 Section in the absolute quantities of the above mentioned constituents and of the preserved nutriments. 8) As regards the absolute quantities of the same constituents and preserved nutriments contained in the combination of the stems cut to a certain uniform length and of the roots, the results of our enquiry have been identical with the results described under 7).1) 育苗中の種々なる摘芯が桑苗に及ぼす影響につきて研究せり。摘芯試驗區は次の如し。 : 標準區…………摘芯せず。 : A區…………秋季 (9月下旬) 先端を摘芯せり。 : B區…………夏季 (8月) 桑苗の先端を摘芯又は摘梢し後, 再發芽する腋芽は之を除去せり。從つて爾後の枝條の伸長は抑止せられしために其の着葉數は減少せり。 : C區…………夏季 (8月) 桑苗の先端を摘芯又は摘梢し後, 其の先端より2-3本宛の新枝條を伸長せしめ秋季 (晩秋蠶期) 新枝條に着生せる桑葉を採葉して養蠶に利用せり。2) A區は標準區に比し全重, 根重, 枝條重, 枝條長, 一定條長の重量, 枝條直徑等は概して大差なきも他の摘芯B, C區は共に何れも減少し, 髓心直徑と枝條直徑との割合は反對に大となれり。3) A區は標準區に比し枝條の折の強さ及び比重に付ては概して大差なきも寒枯は少なく, 他の摘芯B區は折の張さ, 比重は稍々小なるも寒枯長最も少なし, C區は枝條の折の張さ, 比重小にして寒枯長も最も大なり。4) 水分, 乾物及び灰分, 有機物%はA區は標準區と大差なく, 他の摘芯B, C區は水分及び灰分%多くして乾物及び有機物%少なき傾向あり。5) 可溶炭水化合物%はA區は標準區に比し稍々減少し特に根部の貯藏炭水化合物量に於て減少の傾向大なり。他の摘芯B, C區は共に標準區よりも減少し特に根部の貯藏炭水化合物量に於て減少大なり。摘芯區の上記の傾向は標準區よりも着葉數の少なきことに歸因するなるべし。6) 窒素化合物%は各區概して大差なきもB區は稍々大なる傾向あり, A區は標準區よりも稍々小なる傾向あり。即ち窒素化合物%は可溶炭水化合物%と稍々趣を異にする傾向あり。7) 桑苗の根部及び枝條部の諸成分の絶對重量は, A區根皮部及び條皮部の乾物絶對重量, 灰分及び有機物の絶對重量に於ては標準區に比し大差なきも可溶炭水化合物絶對重量及び窒素化合物絶對重量共に稍々減少せる傾向あり, 他の摘芯B, C區は共に何れも標準區よりも減少せり。8) 桑苗の根部と枝條一定長との合計の諸成分の絶對量も亦 7) に述べたると同樣なる結果となれり