because self-concealing is what φύσις bestows from itself as that wherein it itself remains grounded, φύσις prevails here as the jointure (i.e., ἁρμονία), the joint in which emerging and self-concealing hand one another the bestowing of their essences in a reciprocal way. 
In fragment 54 (which we treat as the third fragment), Heraclitus says the following about ἁρμονία, which is the φύειν of φύσις itself:
ἁρμονίη ἁφανὴς φανερῆς κρείττων.
Inconspicuous jointure, more precious than the conjoined that insistently pushes toward appearance.
φύσις is the inconspicuous. Emerging, as that which in the first place bestows the cleared open for an appearing, withdraws itself behind all appearing and every appearing thing and is not just one appearing thing among others. Consequently, within the narrower region of the visible, what typically (and often exclusively) attracts our attention is, for example, what stands in the light and remains accessible as illuminated; over against this, the brightness itself is the unimposing and self-evident medium to which we only pay attention (and then only in passing) when the illuminated object becomes inaccessible to us as a result of the onset of darkness. The human being then fashions a light for himself. As a result of such fashioning, the modern metropolis, even before the war, had already turned night into day by means of a technology of illumination, so that neither the sky nor the lights that belong to it can be seen. As a result of this lighting technology, brightness itself has become an object that can be produced. Brightness, in the sense of the inconspicuous in all shining, has lost its essence. However, brightness, in the sense of the pellucidity of the light, is grounded in the fact that, above all else, clearing and emergence (i.e., φύσις) unfold.
(The modern human is fascinated by this technological monstrosity of brightness; when it becomes too much, he uses the mountains or the sea as a palliative; he then ‘experiences’ ‘nature,’ an experience that certainly  can become boring already on the first morning of the trip, whereupon he just goes to the movies. Ah, the totality of what is called ‘life’!)
108 The Inception of Occidental Thinking