230 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



cell is cut off from the spore-cell and this grows into the first hair-root, 

 whilst its larger sister-cell becomes a germ-tube. In the hair-root the 

 chlorophyll gradually disappears and finally only leucoplasts are found. 

 Germination may take place in the dark, but slowly, and then the first 

 division- wall has any position. If germination takes place in intense light 

 the light affects the disposition of the nuclear division in such a way that 

 the direction of the axis of the nuclear spindle coincides with the path of 

 the light-rays, the two daughter-nuclei therefore lie in this path and the 

 division-wall is at right angles to it. The cell which is turned towards 

 the light is the first cell of the prothallus, the one upon the shaded side, 

 always the smaller, is the primordium of the first hair-root. Diffuse 

 daylight does not exercise a directive influence l . Stahl found through a 

 prolonged culture upon the klinostat that a changing direction of the 

 light influenced division in the spores, that most of them were undivided 

 whilst a number of the others were indeed divided but in an abnormal 

 way to form equally large cells. Similar deviations may be reached in 

 other ways. Buchtien found ' 2 that when the spores were cultivated in 

 concentrated nutrient solution they were divided usually by two walls 

 following one another at right angles, and the formation of a hair-root 

 was often suppressed. 



Kolderup-Rosenvinge 3 has observed in the fertilized eggs of some 

 Fucaceae phenomena similar to those noted in the spores of Equisetum. 

 These eggs have no polar differentiation ; it is only when germination 

 takes place that the distinction between ' shoot-pole ' and ' root-pole ' 

 appears, and the filiform anchoring organs develop on the latter. In 

 Pelvetia canaliculata and Ascophyllum nodosum, but not in Fucus serratus, 

 light sometimes, although not always, exercises a directive influence which 

 corresponds with that described in the case of Equisetum. This is most 

 marked in Pelvetia. In these Algae other directive factors, according to 

 Kolderup-Rosenvinge a difference in the amount of oxygen especially, 

 may also influence the polarity. 



Amongst higher plants the directive influence of light is specially 

 manifest in dorsiventral shoots. 



The branch-system in many Cupressineae 4 , for example, Thuya occi- 

 dcntalis, Thuyopsis dolobrata, and others, which possess scale-like leaves 



1 Buchtien, EntvvicklungsgeschichtedesProthalliums von Equisetum. Inaug. Diss. Rostock, 1887. 

 From this it might appear that in nature the influence of light upon the formation of organs in spore- 

 germination is inconsiderable, yet we must consider that within certain limits germination is more rapid 

 the more intense the illumination and therefore the directive influence of light will make itself felt. 



2 Buchtien, 1. c., p. 24. 



3 Kolderup-Rosenvinge, Unders^gelser over ydre Faktorers Indflydelse paa Organdannelsen hos 

 Planterne, in Vidensk. Medd. Naturh. Foren. i Kj^benhavn, 1888 ; Id. in Revue generate de 

 Botaniqtie, i. p. 53. 



1 Frank, in Pringsh. Jahrb. ix. p. 147. 



