Marx’s Capital Volume 1, Part 7
Chapters 11, 12 and 13 of Capital, Volume 1 (download linked below) which follow the enormous Chapter 10, are short, and require little introduction, because they are straightforward.
They are plain enough to provide plenty of material for study-circle discussion, especially if there are people with work-experience present.
Note that the co-operation Marx writes about here is co-operation in general, whereby people work together under a capitalist. It is not about "co-ops" as such.
The following two excerpts demonstrate how well Karl Marx understood the workplace.
Rate and Mass of Surplus Value
“Within the process of production, capital acquired the command over labour, i.e., over functioning labour-power or the labourer himself. Personified capital, the capitalist takes care that the labourer does his work regularly and with the proper degree of intensity.
“Capital further developed into a coercive relation, which compels the working-class to do more work than the narrow round of its own life wants prescribes. As a producer of the activity of others, as a pumper-out of surplus labour and exploiter of labour-power, it surpasses in energy, disregard of bounds, recklessness and efficiency, all earlier systems of production based on directly compulsory labour.
“At first, capital subordinates labour on the basis of the technical conditions in which it historically finds it. It does not, therefore, change immediately the mode of production. The production of surplus value — in the form hitherto considered by us — by means of simple extension of the working day, proved, therefore, to be independent of any change in the mode of production itself. It was not less active in the old-fashioned bakeries than in the modern cotton factories.”
“When numerous labourers work together side by side, whether in one and the same process, or in different but connected processes, they are said to co-operate.”
“By the co-operation of numerous wage-labourers, the sway of capital develops into a requisite for carrying on the labour-process itself, into a real requisite of production. That a capitalist should command on the field of production, is now as indispensable as that a general should command on the field of battle.”
“The directing motive, the end and aim of capitalist production, is to extract the greatest possible amount of surplus-value,  and consequently to exploit labour-power to the greatest possible extent. As the number of the co-operating labourers increases, so too does their resistance to the domination of capital, and with it, the necessity for capital to overcome this resistance by counterpressure. The control exercised by the capitalist is not only a special function, due to the nature of the social labour-process, and peculiar to that process, but it is, at the same time, a function of the exploitation of a social labour-process, and is consequently rooted in the unavoidable antagonism between the exploiter and the living and labouring raw material he exploits.”
· The above is to introduce the original reading-text: Capital V1, C11, 12, 13, SV - Absolute, Relative, Co-operation.