How middle of ${19}^{th}$ century is an important reference to photosynthesis ?

By the middle of the nineteenth century the keys features of plant photosynthesis were known,that plants could use the light energy to make carbohydrates from $C{O}_2$ and water.
The empirical equation repsenting the total process of photosynthesis for oxygen evolving organisms was then understood as :
$C{O}_2+H_{2}O\stackrel{\text{light}}{\to }\left[C{H}_{2}O\right]+O_2$
Where $\left[C{H}_{2}O\right]$ represented a carbohydrate (e.g., glucose, a six-carbon sugar). .