The other two answers are one direction (+1 btw). I am coming in after your edit to the original question, so here are my two cents...
I define a Value Object as an object with two or more properties that can (and is) shared amongst other entities. They can be shared only within a single Aggregate Root, that's fine too. Just the fact that they can (and are) shared.
To use your example, you define a "Description" as a Value Object. That tells me that "Description" with multiple properties can be shared amongst several Books. In the real-world, that does not make sense as we all know each book has unique descriptions written by the master of who authored or published the book. Hehe. So, I would argue that Descriptions aren't really Value Objects, but themselves are additional Entity objects within your Book Aggregate Root Entity boundery (you can have multiple entities within a single aggregate root's entity). Even books that are re-released, a newer revision, etc have slightly different descriptions describing that slight change.
I believe that answers your question - make the descriptions entity objects and protect them behind your main Book Entity Aggregate Root (e.g. Book.GetDescriptions()...). The rest of this answer addresses how I handle Value Objects in Repositories, for others reading this post...
For storing Value Objects in a repository, and retrieving them, we start to encroach onto the same territory I wrestled with myself when I went switched from a "Database-first" modeling approach to a DDD approach. I myself wreslted with this one, on how to store a Value Object in the DB, and retrieve it without an Identity. Until I stepped back and realized what i was doing...
In Domain Driven Design, you are modeling the Value Objects in your domain - not your data store. That is the key phrase. It means you are not designing the Value Objects to be stored as independant objects in the data store, you can store them however you like!
Let's take the common DDD example of Value Objects, that being an Address(). DDD presents that an Mailing Address is the perfect Value Object example, as the definition of a Value Object is an object of who's properties sum up to create the uniqueness of the object. If a property changes, it will be a different Value Object. And the same Value Object 9teh sum of its properties) can be shared amongst other Entities.
A Mailing Address is a location, a long/lat of a specific location on the planet. Multiple people can live at the address, and when someone moves, the new people to occupy the same Mailing Address now use the same Value Object.
So, I have a Person() object with a MailingAddress() object that has the address information in it. It is protected behind my Person() aggregate root with get/update/create methods/services.
Now, how do we store that and share it amongst the people in the same household? Ah, there lies DDD - you aren't modeling your data store straight from your DDD (even though, that would be nice). With that said, you simple create a single Table that presents your Person object, and it has the columns for your mailing address within it. It is the job of your Repository to re-hydrate that information back into your Person() and MailingAddress() object from the data store, and to split it up during the Create/Update operations.
Yep, you'd have duplicate data now in your data store. Three Person() entities with the same mailing address all now have three seperate copies of that Value Object data - and that is ok! Value Objects are meant to be copied and destoyed quite easily. "Copy" is the optimum word there in the DDD playbook.
So to sum up, Domain Drive Design is about modeling your Domain to represent your actual business use of the objects. You model a Person() entity and a MailingAddress Value Object seperately, as they are represented differently in your application. You persist them a copied-data, that being additional columns in the same table as your Person table.
All of the above is strict-DDD. But, DDD is meant to be just "suggestions", not rules to live by. That's why you are free to do what myself and many others have done, kind of a loose-DDD style. If you don't like the copied data, your only option is that being you can create a seperate table for MailingAddress() and stick an Identity column on it, and update your MailingAddress() object to have now have that identity on it - knowing you only use that identity to link it to other Person() objects that share it (I personally like a 3rd many-to-many relationship table, to keep the speed of the queries up). You would mask that Idenity (i.e. internal modifier) from being exposed outside of your Aggregate Root/Domain, so other layers (such as the Application or UI) do not know of the Identity column of the MailingAddress, if possible. Also, I would create a dedicated Repository just for MailingAddress, and use your PersonService layer to combine them into the correct object, Person.MailingAddress().
Sorry for the rant... :)