358 



LECTURE XXII. 



spite of this we speak of a translocation of the starch, an assumption is necessary in 

 the first place to complete the direct observation. This is in general to the 

 effect that the wandering starch undergoes continual solution and re-formation 

 progressively from cell to cell. In this the activity of Schimper's starch-forming 

 corpuscles co-operates in the cells in question, or, in the younger portions, the change 



is effected by the protoplasm itself It is 

 not necessary to enter more into detail 

 respecting this problem, however, it being 

 only intended to do away with a possible 

 error which might arise from the use of the 

 expression ' transitory starch.' Perhaps 

 a similar assumption is also to be made 

 respecting the translocation of fat in the 

 closed parenchyma. Within the parts of 

 the shoot-axes, petioles, and leaf-veins 

 which are already fully developed, the 

 starch, then, passes from the reservoirs of 

 reserve-materials or organs of assimilation 

 to the growing parts, chiefly or exclusively 

 in that layer of parenchyma which imme- 

 diately surrounds the vascular bundle, or, 

 in many Dicotyledons, separates all the 

 leaf-traces in the shoot-axis from the cor- 

 tex as a closed layer. This is the layer 

 which we have previously learnt to know 

 as the endodermis, and which, on account 

 of this very function, I introduced into 

 physiology long ago as the starch-bearing 

 layer. If a more extensive movement of 

 starch occurs, it takes place also in the 

 external layers of the pith, internal to the 

 vascular bundles ; and, in the case of a 

 very vigorous transport of starch, as when 

 the leaves of trees are being emptied in 

 the autumn, even the phloem of the vas- 

 cular bundles may take part in it. 



In the growing points themselves, i.e. 

 in the extremely small-celled tissue of the 

 apices of the roots and shoot-axes, I have 

 never succeeded in detecting transitory 

 starch or sugar. Both appear in these cells only when they pass over from the 

 embryonal stage into that of extension — of more rapid growth — and as soon as 

 intercellular spaces arise in the young parenchyma. The extremely small quantity 

 of cell-wall forming substance which is made use of in the embryonal tissue of the 

 growing point is in accordance with this. In the growing point itself growth is ex- 

 ceedingly slow, the developing cell-walls immeasurably thin, and the embryonal tissue 



Fig. 240.— Longitudinal section of a germinating bulb of 

 Tulipa pmcox. h brown membrane enveloping the bulb ; 

 k the discoid portion of the stem of the bulb, which supports 

 the bulb-scales sh, sh ; si the elongated portion of the stem bear, 

 ing the foliage leaves /' /', and passing above into the terminal 

 flower ; c ovary, a anthers, / perianth ; 2 a lateral bud (young 

 bulb) in the axil of the youngest bulb-scale ; >• the apex of the 

 first leaf of this lateral bud. This bud becomes the bulb of 

 next year. 7v the roots which arise on the fibro-vascular strands 

 of the discoid stem. 



